I have all 3 versions of bubblers mentioned in this thread~I have a hydrotube (knockoff version), micro-bubbler, and a nectar collector kit very similar to the one linked in the previous post.
The bubbler in the nectar collector kit will hold the most water and is the best for cooling/water treatment effect IMO. You can lay it on its side and it will not leak/spill. You can hit it on an angle, even almost completely horizontal and it will still bubble.
The hydrotube works pretty well as for cooling/water treatment but they leak easy or at least my 4 knockoffs do and they don't hold that much water really. The hydrotubes are great but not really because you have to be pretty vertical to use them. I have 4 and they sit and wait. Maybe they will get some use when I get my Zion.
The micro-bubbler
http://www.shopxhale.com/collections/new-products/products/11463 does not hold much water and the water tends to evaporates after long sessions. I toted the micro-bubbler around with me for a couple weeks but the fun wore off and I realized it wasn't doing all that much. I'm going to try out the e-cig pen ones that have recently come up in the Grasshopper thread, however I'm expecting it to be a waste of $5.
IMO, if you want something to play around with that you don't mind forgetting about then get one of the above. If you want something to use regularly, then get a real glass piece. I haven't tried a D020 yet but I plan to get one of them or a FC-187 or one of the many recommended table top bubbler pieces one these days. Until then I have a glass beaker bong and that gets used every night that I choose not to use the Daisy. Daisy needs no water!