I typically play without technology. That said, I have considered getting rockets with them midgame, not right away. What happens is they need to retreat their AA gun from India and bring it up at least to Caucuses, if it could safely make it to Karelia, great. If the UK has the Indian AA gun in position and has excess money beyond what they can build on London, yeah, rockets are a good buy if playing with tech. They will cause an average of $7 damage each round.
Don’t think of getting a technology as an effective strategy. As the UK, take advantage of your proximity to Germany and blow stuff up. If you have 5-6 transports and several planes, the Germans need to be stacking their core territories pretty high in order to deter an attack. There are no die rolls involved in setting up that threat, those purchases are guarunteed to pay off unlike rolling for rockets, heavy bombers, etc.