The laser cut components are extremely precise, and fit quite well. Quite a bit of force is required to squeeze some of the parts together, so you will need strong fingers, but that is intentional to insure that the parts stay together without glue. The design is very elegant, and quite attractive when assembled. Flexure cuts allow interfering socket joints to assemble, but really hold together. For a couple of the last components assembled, I did use some wood glue, but very little. The sequence of assembly in the instructions could be improved, but overall it works. It is a challenge to assemble, partly due to some very small parts that are a bit difficult to handle. Make sure you are up to it, because it may get frustrating if you do not have at least some assembly skills. This would be very difficult or impossible for a child to assemble. The design is very educational, using a gear train, cams, a walking beam, indexer, and a toggling diverter. A wax lubricant is provided, with instructions on where to use it during assembly, and it is necessary for parts that slide against each other. Kids that play with this will almost certainly develop an intuitive understanding of mechanisms, which can prove very valuable later in life. If you want your child to develop an intuitive understanding of mechanisms, or if you just love cool devices, or both, this is excellent! A work of art and engineering.

This was gifted to my husband who loves to tinker and build things. It took him about 6-8 hours to build. He seemed to have a very fun time putting it together. I took 1 star away because some of the pieces are VERY thin and break VERY easily. There were a few pieces that he had to glue together because they broke and there were not any replacement parts. Doing some research it seems that in some countries this ships with wood glue but not in the USA. Luckily we had wood glue on hand and we were able to fix it with no problem. Once it was all together it works well and is quite fun to play with.

The instruction book was very good and detailed. However, a couple of steps needed 1 or 2 more pictures. When pieces are mated to another piece, most mating needs a LOT of hand strength. When pieces are mated 'midair', like a ball track to another ball track, one needs a very strong plyer grip to mate them. It would be very helpful if the manufacture were to show how they would 'mate' hard parts together. (I attempted to built their crank power projector, and I tried at least 6 times on the interior power train, but it didn't work. So, I decided to try this unit.) I decided to apply a couple drops of cement at some key joints, because some inserted parts didn't really mate fully.

Surely I will maul this thing trying to build it right? Nope. It was a blast to assemble.

I'm gonna break the parts getting them out of the punched wood?! Nope. Easy peasy.

I'm gonna confuse all the directions! Nope. I found one spot in the directions where a diagram was copy/pasted and included a subtle part difference on accident. Only flaw I found. The rest is a master class in diagram and assembly instructions. Same league as say Lego.

I'll break some important piece and ruin it!
You won't. There are certain small "pegs" of wood that can get a bit difficult. These too are etched from the wood sheets. My 11 year old had a little trouble with digit strength getting these pushed in. Kinda ended up breaking one or two of them over while pushing. I helped on a few and showed the technique on the rest.

I think this and maybe one other part had some duplicates just in case. Duplicates unnecessary for anything else.
You won't break anything.

The elevated marble paths going to and fro are a bit tricky to keep sturdy. But they are the last parts you put in and you've gotten quite good at it all by then. A challenging finish.

I'm gonna get some more of these.

The media could not be loaded. The creators of this product did a fine job. It is designed well, the instructions were clear, and we saw signs of changes made to fix problems. We only had a few moments of frustration. All in all, it was a very enjoyable project and it is a high quality design and end product.

My wife and I bought as a project to do with our adult kids over Christmas break, but we ran out of time so my wife and I ended up doing it together. It was a great project for 2 people. We chose to paint ours with watercolor paints. We probably spent 4-6 hours painting and around 6 hours putting it together. The marble track only needs to be painted on the numbered side, and don't paint the "nails" used to hold it together.

Advice for construction:
- 2 people worked out great. One person finds and removes pieces, the other constructs. Switch off after a while.
- The instructions are great. They list the pieces needed for each step on the left so it's easy to get the pieces you need.
- On the tricky parts, watch the video. We didn't watch the video for most of the construction.
- Use the wood tool to press in the "nails".
- It's fun until you break something. There are 2 reasons we broke pieces: not being careful punching out the pieces, and wiggling certain pieces when you put them together.
- Take your time punching out the pieces, especially the notched part of the spiral. Ours broke. The pieces are mostly cut out but are still attached in a few places. Press the pieces lightly to figure out where it's attached and then press right there. Take your time on the spiral. It was connected at its thinnest part which made it super easy to break.
- Most of the tabbed pieces assemble tight. Wiggling the pieces helps, but don't do that on the tower pieces! For the towers, just press straight down. We broke 2 tower pieces by wiggling too much. The most fragile was the tower that holds the divider that sends the marbles in 2 different directions.
- Have glue available. Of all the broken pieces, only the spiral was a big deal. Ours broke right where the notch connects to the post. We just put glue on the post and connected the pieces and it was fine. We also glued the washer like pieces on the stairs to keep them from falling off, and one section of track that was a little loose fitting.

Other notes:
- There are extra "nails". If any punch out bad, just use another one. We only had one that punched out bad.
- It comes with 10 marbles. 5 is the perfect number. With 10, 2 marbles will go up the stairs together, which we didn't like, but then they take 2 separate paths down, which was pretty cool.
- Painting was fun. It doubles the time of the project, but looks so much cooler when completed. We did not obsess over colors, and there's only a few places where we wish we picked a different color. Watercolor paints are the way to go. You can still read the numbers to assemble. Acrylic paints are more expensive, would flake off where the pieces rub, cover the numbers, etc.

I would not recommend this project for kids unless they are VERY patient, and adult help would be a good idea. I would absolutely buy this again or give it as a gift with some watercolor paints.