They are really good. My kids thought they were noisy but they are in fact very quiet when they go past, can hardly hear a thing. Simple yet so effective.

 what do they think about chain tension in it? as I know, it's not tensioned at all, so the bottom chain line isn't too loose? how does it feel on bumps?

 Chain tension is not a problem. A chain needs to be the right length rather than tensioned, the derailleur will do that anyway. A chainguide is there to keep your chain on the chain ring which these do very well. To me these are much quieter than many of the other guides out there and so simple to set up. Both my kids have run these for 5 days of DH at a race meet on rocky terrain and no problems at all. They and I like the fact that they are simple in design yet very effective. They've smashed them with a few rocks and still going strong.
I rate them and I'd say grab one to finish of your F44 with one

 your're right about that derailleur is tensioning chain anyway, somehow I forgot about this thinking about this chainguide. in other way, I just used to fact, that bottom line of chain is going up to sprocket, but probably I'll run with this new one to see the diference (the first one that is heard, that you hear almost nothing )

 You may think it is a bit noisy but that is because it is aluminium and not plastic. The plastic must absorb the vibrations whereas these don't. But like I told my boys, when they first went past me I was surprised how quiet the whole bike was.

 As I spoke to Pawel at Zumbi this chainguide is quiet in deed. I see no other way like to get one and see myself