I bought the compression tester as well,
about a week ago.
I used it one time (with 3 rounds of testing)
and it worked fine!
(I feel I already got my money's worth!)
I drilled out the case where the VW/Audi adapter sits,
so you can keep the threaded piece on the adapter
(I wrapped it with Teflon tape and tightened it really well)
-Brad