Nah, the longer Defender of the Front (a nickname I coined for that thing's damn near impenetrable front) stays off sale, the less rage it will cause. Apparently, the only thing that it is worse at than the IS-3 is gun handling (infernally bad, probably the worst in the game), and for the KV-4, side-scraping (pike nose, so to be expected, the pike nose tanks are horrible at frontal side-scraping but better for reverse).
Mutants I could care less if WG sold it or not. I played many games where pre-order bonuses were later included as DLC, so I wouldn't be so salty if I owned a Mutant as a pre-order bonus (which I didn't because it was just bloody expensive). The whole deal about pre-order is that you are guaranteed to get the game once it's released by paying in advance, and get a bonus which players won't get until much later.
I wouldn't use an Object 252U tbh; one, it's just not fair to T6s, two; I'm not a good brawler (a result of driving mainly glass cannons, the Sherman Jumbo was literally the first tank I had that can brawl effectively, and I used my SU-122-44 as an ambush-TD), and three; I couldn't stand that god-awful gun handling.