Navigator kits: They did the IS-4, T-10 and T-10M. I have the IS-4 and T-10 kits. They are decently detailed. That is all the nice things I can say about those kits.
For the IS-4 from Navigator, lots of the kit parts are based on the Tamiya IS-3 kit (since the IS-4 was based on the IS-3 parts as well...like the running gear, etc.) The white metal pieces, while nicely done, are white metal and a serious pain to deal with. The resin is brittle, hard to unwarp (yeah. lots of warp in these kits) and hard to sand. I wrestle with mine every so often to remind me how much easier I have it with plastic kits!
With a LOT of work, a lot of patience, and a LOT of after market, the Navigator kit would make a impressive, HEAVY model. I think I will buy the Trumpeter kit, save the time, and thank the modelling gods.