the better ones are just a twist fit, although i ditched mine as it wouldnt stick where i wanted it on the screen due to the curve in the screen...dont actually know where it ended up....
I had this same problem with my twist fit disc holder, i ended up putting extra sticky pads on it and just persisted with it, year and a half later it's still on there. Twist fit is much better than the allen key ones as you will end up loosing one of the screws.
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MG ZS 2.0 TD a work in progress.
When I fit mine (4 cars now have them) I offer the holder up to the screen to see where it touches and apply the stickers to those points. The worst part as getting the pads off.
With the screw on one we had in the ZR I had no problem losing the screws - I lost the allan key
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Former custodian of the legend that was FE54 - RIP