Hi
1) they are not cheap - the mini-versions are typically £150 - not sure ones you are quoting.
2) They need careful setting-up - but this is a "precision" instrument, so it's worth getting it right.... then the settings will be fixed. If you change lenses, you need to adjust again.
3)It needs a certain "skill" in use - this may take some while.
It's not an instant fix, like screwing on a CU lens.
If you are prepared to take the trouble they can be Magic - but so far I've avoided buying one as I'm hoping to make a crane soon to go on the heavy duty tripod.
+There are some Tutorials on YouTube that may help you with setting-up.