I actually liked this tool very much. It cut my edging time by 2/3. With the ease of refilling and the ease of application It was quite an experience. It took one refill to get a hang of how long to hold the trigger, the fuller it is the faster the paint comes out.
However, I gave this 3 stars because of the fact the pad does not edge very well around outlet/light switch covers, trim, ceilings, or base boards. If your painting with the sane color you might be able to get around it but it leaves almost an 1/8 of unpainted area, it also obviously won't fit in areas smaller than the 3" pad.
So in the end I stopped using this tool for edging because there's no point in using it if I still have to go back through with my paint brush to cut everything in.
However, to it does make a good paint siphon for my edging bucket.

Got this product today and excitedly ripped it out of its box ... after reading many reviews I was curious as to some of the complaints on the negitive reviews ...

TLDR:
Test with water to get the idea without the head attached and you will see how different pressure on the button will really differ the amount of liquid expelled little pressure with quick release will drizzle out some small amounts of liquid ... big long press will blast it out like a super soaker ...

Full review:
After unpackaging the product I immediately decided to try with water here are my results:

First test:
Pressed button and pulled back trigger let go of handle while still holding trigger and immediately it emptied the tube into the sink at super soaker strength kinda like a little water gun you keep in your boat when going down the river to get your friends ...

Second Test:
Refilled let go of trigger button then let go of handle and it held the water quite well. Then pressed the button half way down and held it there ... much less pressure however the water came out quite quickly and wasted it all in a matter of about 5 seconds...

Third test:
Fill it again let go of button and then handle, which again held the water with no leaks ... then I lightly tapped the button with my thumb and just a tiny bit of water came out ... this is how I'd imagine you'd use it while painting so I practiced the pressure a few times to get used to it until all the water was gone which lasted a few minutes of little tiny squirts ...

Fourth test:
I filled it, realeased button, let go of handle ... again no leaks ... this time I used light pressure on button and watched the water slowly drain out which took about 45 seconds ... so not ideal if you just want to keep constant pressure on the button and streak across your wall as you'll be refilling about every minute and you'd have to work at break neck speeds to not cause drips ...

Conclusion:
I was learery due to the negitive reviews but this tool seems great for what it's used for ... I recommend practice on the pressure with water before actually using it to get the idea but I can see how jamming the button all the way down even in little quick bursts could cause some major paint problems on your wall ... but with a few minutes of practice you'll quickly see how it works and be able to quickly tackle your edging problems!

Thanks for those who took the time to read this and I hope it helps!!

This product makes painting a lot more fun. It is very simple to use and easy clean up.

This tool is great for painting. It helps you cut in the walls at the ceilings and you can use it to paint the walls in general. I don't use brushes or the long rollers, just this. Works great. Can be cleaned out and re-used again.

this was very hard to use, I read the limited directions and watched a few u-tube videos but never really grasped a good way to hold or fill the product. It ended up being a timley mess. I wanted this to work for the ceiling, I hate cutting out the ceiling but it really didnt do the job.