if you look at the picture on thingiverse:

You are using the same channel that the extruder carriage uses. Unless you are right down by the base triangle you can't use those channels to attach things as it blocks the carriage going up and down.
And if you put the holder in that channel as low as it needs to be, then large reels will be resting on the ground, which you don't want.
Also the shaft where you put your filament is much too large. I have a number of filament spools where the centre hole is 10-12mm.
Also by angling the shaft on mine, you don't need a large block at the end to stop the reel falling off.

So my design:
1) does not block the carriage
2) No chance of the spool falling off, also the spool is slightly angled which hugely reduces the chance of filament wrapping round the shaft and jamming the print.
3) is mounted on the opposite strut, so the filament keeps taut and won't catch on anything or tangle.
4) the angled shaft will also takea lot more weight, so could be used for 2-3kg spools
:-)



Print one of mine and try it: I think you'll find my design and placing is a lot better. It's the little things that make the difference.
You're welcome to use it and stick your logo on if you like, just give me design credit.