I have gone from Glass Lily Pipes, Pollen type diffusers, in tank Aqua Do and ADA ceramic diffusers, to UP Aqua in line diffusers. I tried a Bazooka type in tank diffuser I brought back with me from Hong Kong, it worked for about two days and then wouldn't work unless I cranked the pressure right up which finished up blowing the tube off the diffuser, water in the tank was blowing round like a bloomin washing machine.
I have gone back to the UP Aqua In line diffuser, although to be honest even that has fluctuating performance, its a right pain the a$$!
There was some faults with the latest style of in line diffuser, the new model where you could unscrew the ends and replace the ceramic tube, the plastic they used was splitting causing massive leakage of Co2. I complained to UP Aqua who have since sent me some in tank ceramic diffusers to test. They are the same as any other ceramic diffuser, they work for a week or two and then get clogged up.
UP Aqua also sent me some new model in line Super Diffuser to test but it was a 12/16mm pipe fitting so I couldn't use it. I got back to them and they are now sending me the 16/22mm version to test instead.
If you want to see what they look like see the links below for details.
http://www.up-aqua.com/00-dm-page/00up_co2-118-1.jpg
http://www.up-aqua.com/00-dm-page/00up_new-diffuser.jpg
Regarding flow issues, if you are going for a reactor, which I think are probably the most efficient, you either have to bite the bullet and take the hit on the flow output from your filter, or set it up on a completely separate filter, which means more expense and hardware in the cabinet.
Hope this helps,
Cheers,
Steve.