Do you still use that beamer?
I'm tired of mine. I'm considering a wilflife mag beamer kit. Costs twice what the better beamer is, but, it's not flimy splastic, instead, it's floppy rubber. I dunno. Considering trying it. My longest is 600mm though on 1.3x crop (1D III) which is nearly 800mm FOV on full frame.
My main concern is distance to subject. I find that I have to be quite close for ETTL & HSS on the flash to matter, at all, with the better beamer.
How close do you have to be before your flash no longer does anything?
That is my "Old" home made beamer on my DIY bracket - these days I use a real BB, but it was a bit pricey at £10/$13.
To be honest I don't use it often - well pretty rarely really. I use it mainly to freeze motion or help highlight the subject a touch. As I simply do not understand flash photography I simply use it in Manual at low power and guesstimate a little underexposure - seems to work OK.
I have been using it at 8 meters + and it seems OK, I haven't used it beyond about 15 meters as the subjects would be too small for poor light photography. it is rarely used but now and again it is handy - if I have remembered to bring it!