All of the ones I've seen under $50 are cheap Chinese knock-offs. That does not mean they are useless, just that they don't have the same tolerances that the originals have. The link you posted of AM leonard at $450 is clearly an original design high tolerance tool. I got one of the Chinese knock-off versions of this design. For what I paid, I'm pretty happy. The blades make nice cuts, but the cast V shelf can mar softer wood. I put some insulating electrical type on mine as a cushion. It helpeyou d a little. One of the pins broke this year and I had to replace it with a screw. I've had pretty good success with it. About the same as with my W&T, but it is much faster.
The key is having scions/rootstock in the right size range. This may be true for the high precision models as well. I don't know, I haven't used one of them.
If have well matched scions and rootstock in the right size range for the tool, it can be very fast and effective. Here is a link to another forum thread where I first found out about this one:
https://growingfruit.org/t/zenport-grafting-tool/19713
Thanks,
Jack