I think I now have an opinion and some insight to offer on the question of a proper tank at 500 pts. I think in an open tournament environment, go for it. Looking at the stats on the FlammHetzer, that is one limited vehicle. You are playing enormously off the medium tank rating (9+ to damage) and opponents' lists lacking adequate AT to stop you (also the reason I am against it in learn-to-play environs). Sure, you may have beautiful games where you torch 3 squads off the table over 4 turns and still have the flamer available. But if that flamer is not lighting the world on fire (heh!) then you just paid a colossal premium for an MMG. That plus the limited range on the flamer means you want to get relatively close and in the opponents face. Maybe not point blank, but much closer than if you were an assault gun with a howitzer. Combine with the 45 degree arcs making flank and rear much more prevalent than in FoW and you have a recipe for tension with anything that has any AT rating, whatsoever. Particularly in later rounds, when the Hetzer is in close, that lack of order dice leads to a high chance of the nearby infantry going first and getting a decent assault off, which with tank grenades can easily endanger the tank. And the +1 to damage courtesy of being a flame tank makes it even scarier. If the tank decides to skulk back where its flanks are safe and most AT is at penalty, well good luck with that 150 point MMG and enjoy pressing forward with inexperienced infantry. Without the tank meaning units on objectives I predict a lot of fire will fall on those squads. Field promotion to regular or not, they will accumulate a lot of pins and probably a lot of kills very quickly (just to get upgraded they have to have at least one pin and one kill against them, so hello order test). On top of all of that, some punk with a Bazooka can obliterate the Hetzer with a single shot for outside the Hetzer's move and spray range. Basically, in an open and competitive environment I think the FlammHetzer is a perfectly reasonable gambit to take and the points are probably fair on it (actual play-testing lacking, though).
In a learn-to-play environment where the emphasis is placed on learning the rules and building core forces, I would consider bringing one rude. As I argued above, the gambit is heavily predicated on out armoring your opponents AT and their not knowing how to take down such a beast. Additionally, the missions are most likely to be basic killing missions to learn mechanics where the penalty of not contesting objectives is limited. In such an environ it is fair to assume most players, especially newbies will field highly generic and basic forces that are less likely to have the kit to threaten a medium tank. So, I think it to be against the spirit to pose such a risk for offering a negative play experience to the other players.