Can you use an e type front mech on any frame or do they have to have the locating screw? Looks to me like the one I have would flex a bit too much if the locating screw is not fitted.

You can but it's not ideal – without the locating screw, the plate can flex more so shifting isn't quite so crisp though it does work in my experience.

That said, I'd never use one out of choice since they're top swing only which tend to go rattly much quicker than conventional mechs.

Oh and you need to do the BB up very tight to make sure that the mech doesn't spin around

Thanks Clubber – think I'll give it a miss then.