Easy to use as long as you have the fuel cell cut out to be about the size of your hand. As long as you can physically crunch the foam down to the size of your fist (which most any adult should be able too I'd guess), then you can crunch them down. Slot them into place and they will swell up to the size they need to be within a split second. Crunch the next one down and repeat.

So far, they seem to be holding up to 110 octane racing fuel. Haven't noticed any break down into the fuel filters at this time.

So all in all, for the time it takes to get them (lightening quick). How well they are to shape and get where you need them. And how they hold up to fuel/liquid actually interacting with the foam. Everything seems to be as it should be. We used the foam blocks in our fuel cell in our dirt modified and we do think that they are stopping the slosh nicely and do not allow for extra weight transfer from the gas sloshing back and forth. Works exactly as advertised.

Perfect size for my fuel cell.

Used for aquarium filter

My race plans for the 2020 season include running my 2019 ZX-10R in MotoAmerica Stock 1000. One of the requirements is to fill the tank with anti-slosh material. I looked at a few different options to accomplish this including many separate small foam blocks you stuff into the tank until full. Buying pre-cut foam blocks was considerable more money. I bought these and a very sharp (yet inexpensive) kitchen knife cut these into small 2x2x4" block and stuffed them in. I believe it took just over one piece to fill the tank. Plenty left over for another bike or two. They also cut very easily with the large kitchen knife I bought.