Agreed, I over simplified. If it were that easy Zgemma's would be supported and they're obviously not for a variety of very good reasons. VIX is nice (i'd not be on a vix specific forum if I wasn't a fan), but ATV and PLI are also very capable images so the way I see it, it comes down to this:
The HD51 is almost the same price as the solo2, but 3x faster, it's got more flash and a decent dual core ARM CPU, if you aren't bothered about FBC (saves an LNB upgrade or additional dish/new LNB) and can accomplish whatever usage you require with ATV or PLI then the mutant is a great deal. At some point WoS may stock them (the current mutant section seems like they're selling off stuff rather than supporting them) and VIX may support them at some point, it's very, very early days yet. The other options are wait 3-4 months or spend £110 more for a Solo4k with FBC and £60+ on an LNB upgrade, more like £85+ if you need another dish. FBC is tempting, but including a spare dish and LNB that's almost £200 extra, you can almost have two HB51's for that.