Bob Henson wrote:

Again, it works just fine - it would seem that Microsoft only has it in
for Classic Shell. Albeit not as configurable as Classic Shell, it does
the job nicely. I'll leave that one on and carry on using it for a while.

Do these other shell enhancers/replacements also include modifying
Windows Explorer? As I recall Start8 did nothing to Windows Explorer,
just to the Start menu. ClassicShell can also modify Windows Explorer
to be more retro. ClassicShell can also modify Internet Explorer. So
ClassicShell is doing more than the other Start menu only enhancers
which means there could be a conflict with ClassicShell and something
other than the Start menu it modifies.

http://classicshell.net/forum/viewtopic.php?f=12&t=3349

So there had been what were deemed "minor" issues within builds prior to
where Microsoft blocked it via the compatibility service. That you
didn't encounter or notice those problems doesn't mean that ClassicShell
was okay under Win10 TP. Maybe something not so minor came up. The
others not getting blocked could be that they are not on Microsoft's
radar or they do not cause the problems that ClassicShell does (which
does more than the others).

To be fair, I wouldn't be surprised if Microsoft purposedly blocked ALL
such shell replacements. The tech preview version is to be tested for
what it is, not what it be twisted into. You're supposed to be testing
the tech preview and providing feedback on that. Program compatibility
is a part of that testing but shell replacements are hardly mainstream
and detract from you testing the OS features themselves.