I'll have to check but I'm pretty sure that the print is not being skewed at all. It doesn't appear to on my metal simple which is about 2mm off front to back. Printed test cubes show no apparent skew at 2.5cm height. Your idea would be that it is only compensating on z but compensation on all three axes is just as easy to do with firmware code. If you look at demos of it on youtube you will see that they are printing on significantly tilted beds that will obviously show skew if present. As far as price goes, the parts to do this yourself are less than $10 on amazon plus a few printed pieces.