Hey there...
Just wanted to share my experiences. I own both the Sticky Brick Junior as well as the FlowerPot (with all 3 currently available heads). I do not have the HydroBrick, but the Sticky Brick Junior has built a well-earned reputation for being the most "cloud heavy" of the Sticky Brick lineup... so results should be similar to the Hydro.
I love both vapes beyond all reason or words.
For a quick "tune-up" or semi-portable travel vape, the SBJr is incredible. I have no complaints whatsoever with it. It truly is the "Vaporizer of the Gods", as my .sig line says!
For the best desktop experience (through glass) that you are ever likely to run across, the FlowerPot is pretty much IT.
Differences? The Sticky Brick Jr. is not really well suited for water pipe use... it does work with the seperately sold Gong adapter, but it just seems too "finnicky" without direct mouth feedback... I end up combusting too often when using the SBJr. with glass. Maybe other users have perfected SBJr. use with glass pipes, but so far that particular skill has eluded me. Since the HydroBrick is designed right from the ground up to be a glass based vape, you probably won't have the same issues with it that I've struggled against with the SBJr.
The FlowerPot is obviously less portable and more equipment intensive... but WOW! Does that equipment DELIVER!!! Especially through glass with minimal diffusion... for herbal vaporization just like God invites guests over for, the FlowerPot "ShowerHead" vaped through a J-Hook simply can't be beat for flavor and effect!
You won't go wrong with either and (in my opinion) you should eventually buy both... but I would without hesitation suggest the FlowerPot as a first buy, you will NOT regret it!