Retro DIY CPUs

Speaking of Z80 build-it-yourself boards, has anyone had any

experience with the Russian PDP-11 clone chips, e.g.
KH1801BM4?  How 
difficult are they to obtain and how compatible are they
with the 
real thing?  The photos of ones that I've seen have date
codes in the 
90s, so they can't be that rare.

Cheers,
Chuck