On some non-recommended head units, there have been reports of bootloops, whenever the stock launcher was changed to a 3rd party one.
So far it looks like this is only concerning some older generations of SD450 and AC8227L devices. It looks like the issue was fixed with newer software versions. But I couldn't confirm it yet, neither do I know which versions are safe. Therefore, if you do not know how to recover your device, it is NOT recommended to install any 3rd party launcher on SD450 or AC8227L units.
If, after installing a 3rd party laucher, you experience such a bootloop, be eased. Your device is recoverable.
You have to get into the recovery mode of your unit and reset the device to factory settings. Please contact your reseller or refer to your user manual for specific instructions.
I only recommend installing the launcher on SD662, SD625 or PX6 devices. Generally I'd not advice buying anything else then a SD662 or SD625 powered head unit.
Note: This does not apply for E39/ E46/ E38/ E53/... head units.