There are two main main issues to consider before doing so:
1) The most important issue is that we cannot recommend using low voltage LED lamps with electronic transformers used with halogen lighting - they are not designed to give the appropriate current for high power LED's and the long term life of the lamp will be compromised - this is why our MR16 LED lamps are supplied with drivers. In our opinion a low voltage LED system with the correct driver will be significantly more reliable that the mains voltage GU10 based systems where the driver is much smaller and is a necessarily compromised design.
2) The second issue the amount of light - low voltage halogen lamps are MUCH more efficient than mains halogen which means that whereas a 4.5w led might replace a 35w mains halogen, it will only replace a 25w low voltage lamp. We've seen companies claiming that 12v lamps with a 150 lumen output can replace a 50w halogen! Nonsense - not even close!
Switching to Mains Voltage Lighting
If you are thinking of changing away from low voltage halogen lamps to LED then why not consider moving to mains voltage LED - it's easy and here's how to do it:
1) Remove your existing transformer and connect a GU10 lampholder to the cables
2) Thread the lamp holder back through your existing fitting (no need to change the fitting)
3) Add a GU10 mains LED.
Simple!