well, if someone were to simply show up looking for a pick-up game on vet's night and all of a sudden they spring a baneblade or other super heavy on me, i'd no doubt be inclined to argue that my opponent can't use it!
super heavies are usually meant for huge games and/or fun senarios and such - not to be included as a major surprise advantage!
flyers on the other hand aren't really that bad... sure you only ever hit them on a 6 (unless you have an AA mount!) but overall they're not that over powered... (best idea is to simply ignore it! a flyer can claim/hold objectives for example unless it has VTOL hover mode or similar - at which point it's a sitting duck!
)
most forgeworld stuff i see is also codex-legal stuff anyways! it's just that most players who can get their hands on it, perfer the much more finely detailed resin models! (and honestly, who hear doesn't want some forgeworld stuff for their vehicles!)
cheers!