I use Cyrix 166 with linux 2.0.30 with no problems. I have tried to add
cyrix patches to kernel, but I can't enable 6x86 variable sized paging
mechanism (VSPM), because it reboots immidiately after decompressing
kernel (I have 32MB RAM).
But without VSPM (or even without cyrix patches at all) it runs very nice.
I'm am glad I've bought it and I can recommend it to you.
$ cat /proc/cpuinfo
processor : 0
cpu : 586
model : 6x86 2x Core/Bus Clock
vendor_id : CyrixInstead
stepping : 1 rev 7
fdiv_bug : no
hlt_bug : no
fpu : yes
fpu_exception : yes
cpuid : yes
wp : yes
flags : fpu
bogomips : 132.71