I use it but not all the time, usually when I don't have enough hands for treats, clicker and other props the clicker goes

I've found it's very good for getting the timing right and the click confirms they have done what you asked. I've tended to use the clicker to teach a command but once he's got it I don't use it much, just treat and/or praise.

I started using the clicker 2 days after we got our pup, so he was 8 weeks old but I think it's something you can use at any age. He could sit within a few hours and lie down within a couple of days. I'm new to dog ownership so I'm not sure if that's rapid or not.

It's a postive training method so there's no harm in trying it.