i have to say the Invert mini looks nice and for the price .... hmm , out of the markers you mentioned if you had a spare £200 or so which would you suggest?
Ide say go for a planet eclipse marker, but im slightly bias, but the last few markers ive had are planet markers, they are for me, a much more user friendly gun than the others i mentioned, for £200 i would be looking at etek 3 and 4s, these things are bomb proof, and incredibly easy to maintain, if your not to clued up with fully stripping your maker.
They include a full set of allen keys and every oring you'll need as well as a very clear user manual, as well as a decent carry case for it all instead of a cardboard box.
Minis are good markers as well mind, ive had two and ive never had an issue with either of them, although theres guys that play at our local site, whove had nothing but trouble with them.
Buying a marker is pretty much like buying a car, if you buy one from a young lad whos banging on about all the "upgrades" hes installed, you know its more than likely been hammered, not looked after or serviced, just lots of shiney stick on bits that do nothing.
bit of further advice, 9 times out of 10 any upgrade for any gun will do next to nothing, bolts/boards/spring kits/etc etc etc, dont waste your money, once you get a marker, invest in a decent bottle with a decent reg, a decent barrel kit and your away, a hopper is a hopper , as long as it feeds at 12bps its fine, everyone will say buy a rotor, its more for show, a v35 halo etc will get you playing, and will keep up with the guys with rotors.