pretty good 'TV sfx'

I feel that the TV series sfx were in some important ways superior to the later theatrical film. The Martians just looked "more real" to me, as did the mental images of the Martian race purge.

In any case, I think that the Martian "locust-crabs" in both of these Quatermass films are some of the very best aliens ever conceived and executed. To me they look like real biological specimens and I wouldn't change anything about them. Of course, they were all dead, so no animated sequences were required for close-up action. The Martian purge doesn't really count because there are distance shots, swift cutting and no real close-ups of the Martians as they would move normally, in non-combat situations. These days, puppetry-cum-cgi would handle these little critters perfectly. But that's NOT an endorsement for any remakes.