I'd never use TinyXP or MicroXP as a Windows operating system - I have my original CD's for that, plus it's kind of pointless.
But for the purpose of only running WinUAE and Amiga emulation on an old piece of junk or specific purpose ITX build, I think it's fine. After all, we are talking about a hobby system that may not even be connected to the net! It's just a project, probably an offline one.
MicroXP has not got any networking software included anyway - it's been ripped out - and you can install a third party firewall and only allow WinUAE to have outbound and inbound traffic behind a router.
To use a full blown XP with updates and virus checking kind of negates the idea of building an Amiga x86 where you want to forget XP was ever installed. This thing would never get anywhere near communicating with my other PC's! Just a little hobby side build which I can pretend is a classic Amiga machine.