Yeah I'd assumed they were a gimmick as well so I've never been bothered, but the Craft Beer Channel recently did a video on the cheap knock off ALDI version of the Fizzics and it piqued my interest:
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(skip to 11.35 to see what got me interested and to cut through him being a divvy).
I picked up a cheapo Fizzics after that as I thought it had potential. If you aren't that arsed about the type of pour, mouthfeel etc then you'll use it a few times and sell it. If you are, however, a big foam beer weirdo, then they are kinda class.
Basically you put the beer in it, it creates a vacuum and pulls the beer through it, and allows you to push back on the handle to create pure foam. Means you can create really smooth, creamy beers at home. Obviously it can't ever compete with proper kegged beer but it's class that you can put anything into it and make it so much better than simply slamming it into a glass from the bottle. I love it.

Aye we still get out through the day by he's total carnage now so it's not even worth the hassle going into small venues unless he's asleep. He can't sit still for more than 10 seconds before wanting to run off so we're much more selective about where we go. He'll get better when he can hold his attention beyond the next thing in his eye line.
It has meant that I'm back to valuing the quality of drink at home as I'm probably only having 3/4 a weekend. Great that this Fizzics has enhanced those beers which is why I'm a huge fan. Really looking forward to getting an impy into it but can't be arsed with the fuzzy head it'll give me when I'm up at 5am the next day playing the bongos and throwing plastic eggs around (don't ask).