loads knocking around on e-bay, Ive read (somewhere) that the inexpensive chinese ones do the job?? anyone got one, or had one??

Very good for what they cost and easy to fit .

I've got the Puig universal deflector on both my Tmaxs, and on both give an improvement (ie reduction in noise). It seems that the worse the screen, the bigger the improvement! It transforms the mk3's appalling screen to be quite reasonable, whilst it makes the mk6's screen (which wasn't too bad to begin with) a bit quieter. My experience is that such deflectors always bring an improvement, though how much of course may vary!
They don't seem that complex in design (with the possible exception of the Laminar Lip) so I guess there is no reason why a Chinese ebay special shouldn't work - though the wind forces are quite high, so make sure it's securely fixed.

I'd go for the 2 hinge one over single hinge type it fitted k7 burgman okay

I have a single hinge one and it works a treat but I'd agree with Julian about the 2 hinges.

I must admit I prefer the ones that screw through the screen. I just don't trust those hinge mounts, without having any particular reason or experience why!

There's rubber inside metal bracket clamping screen both sides and 2 grub screws on each hinge seem solid enough to me .I tried to pull mine off didn't budge.

I have the single-clamp jobbie which was kindly donated by kayz1. It has been on the Nmax since Feb/Mar '18. The only thing I would comment on is that the cheaper deflectors will not be of the high visual quality you'd get with quality sceens and more expensive deflectors. There must be a reason the Givi deflector costs 3x as much.
I'm not complaining about mine because I don't have to look through it. But cheers, once again kayz1! Forgot to mention that mine works very well as a deflector for 125cc speeds.

Just return to the magestic sh300i

Got one on T-Max and one on MP3 for over a year now. Both from Ali Express. Found them to be well made, never required re tightening and worthwhile as far as wind deflection and some helmet noise reduction.