I only have the Type Heaven. I find the rubberizing or whatever they've done to the keys more than offsets any cheap feeling the ABS plastic might impart. All of the keys are rigid and I don't detect any appreciable wobble. I haven't tried any other PBT keys but those on my Model Ms and Unicomps, which probably aren't similar to those on the Realforce, but compared to those I don't find the Type Heaven keys lacking.
I have seen in some videos where the Realforce has a deeper timbre to its "thock" and I can hear that, though mine in isolation doesn't have a high pitched sound, it's still a dark, low sound that I like.
If the Realforce is better, I should get one, because the Type Heaven is a very solid, pleasant keyboard.