For me if you are going to use a registry cleaner, use one that is only a registry cleaner and not some jack of all trades that just happens to include a registry cleaner, use a specialist tool for a specialist task.

If you are regularly trialling software (like many on this topic ;D), you ‘hope’ that they clean up after themselves unfortunately that isn’t the case for many, so you just trust to luck that what they leave behind might not have an impact on your system (like certain AVs which shall remain nameless), personally I think not.