The big problem is lack of recoil. I speak from painful personal experience, having lived in the UK for 11 years and finding something realistic to practice with was hard. Closest I could get really was a deactivated pistol using a Beamhit system. Everything else just didn't feel right, including air pistols and actual handguns, the stupid long-barrelled revolvers people in GB are now forced to use.
There's a guy in Mississippi who makes a compressed air system for guns to simulate the recoil, together with a laser.
If you use a .45, I think the best bet would be to simply practice with a 9mm top-end on your .45, 9mm is a lot cheaper and it still has recoil. Or get a 9mm 1911 with an aluminum frame maybe?