Hard to figure out but seems to work fine

Well made under gravel filter. I used it in a 40 Gallon tank I'm just starting to set up. I used three of the four supplied bases and my tank is 36 inches long. Everything was there taped up. The plastic is perfectly adequate for the job. There is no need to go heavy duty on these parts. They will last decades as is which is more than can be said for the HOB filter variety. Just getting back into the hobby and I learned my lesson well when the HOB filters became the preferred profit makers for filter companies years ago.

Once a very popular filter, actually it was considered the best at the time, it is now frowned upon and is no longer considered the best filter to use. This is not because the filter is not great at what it does, its just that the definition of "best" has been refined for modern times. "Best" is now defined by a product that requires regular purchase of filter media to get the "best" profits for companies producing them. They are also "best" at wasting resources and adding to landfills. They are also "best" at unreliability being at about five years or so.
So if you want the "best" available today in terms of all those things, don't get this.
This filter won't create waste for land fill, won't fail spectacularly, won't require you to keep the filter companies profits afloat, but it will filter your aquarium crystal clear for decades without issues or monthly costs. Just understand how they are meant to be maintained (leave them alone!) and you are good to go.

This review is based on my experience, from the 70s to now. All my aquariums start with a UGF and power heads as a basic foundation. I say basic because these are so simple and easy to use and very effective.
These are huge biological filters.
Once the beneficial bacteria colonizes in the space underneath the filter plates, these function for many years with NO maintenance. No gravel cleaning.
Contrary to popular belief, they NEVER GET CLOGGED. EVER!
Yes, you can have a planted aquarium. One does not effect the other.
These seem to have become less popular, almost demonized on the net by all these so called experts. As a matter of fact, I had to buy on Amazon because no one carried them. If you don't understand the nitrogen cycle, you simply won't get it.
If you're smart, you'll always start with a UGF.

Was a good price for a 55 gallon undergravel filter. Supports the gravel and rocks well and has not broken a panel. Seems to be well made. Would buy again

I knew this item wasn't going to be anything special, it is a great price after all. One thing which I should've notated before buying it, is that it comes about 2" short from covering my tank width and depth. The dimensions are notated in the description so be sure to read them and make sure it fits your needs.

The plastic feels very cheap, but the product was in tact when it arrived and all pieces were included. I was happy to see that it came with four filter tubes and not just two like most pictures show. I am also impressed by how tall the tubes reach (3-4" from the top of my 55g). As a side note, it's not really a big deal, but my pleco really doesn't like the tubes in the middle of the tank, since he can't go behind them.

The only thing I dislike about this pennplax filter is the rubber clips that are supposed to hold each of the four plastic trays together. The clips are too loose, and as soon as you turn it over to put it in the tank, they just fall off and the pieces come back apart. (you could easily break one of the trays if it hits the floor, they aren't very sturdy). This wouldn't be a problem, but as I notated before, the setup width is about 2" less then my tank. That being the case, it would be nice if two pieces would stay together on each side, preventing rocks from getting underneath as easily. I will have to come up with something to hold them together, kind of hard since pretty much every idea I can think of involves metal or glue, neither of which sound like a good idea in an aquarium.