I've used straight Windex and straight alcohol to clean my gun. Both work quite well. I have also used, and still do from time to time when I need the convenience, plain old winshield washer fluid. It works quite well, too. But when it comes down to it, you just can't beat plain old hot soapy water for cleaning a muzzleloader. It's cheap and it is effective.
As for the brake cleaner in a spray can....yep, it's good stuff. However, it is best for cleanng modern firearms. You just can't beat it for getting the "gunk" of burned powder and lead bits out of a .22 rimfire. They are famous for building this crap up in their actions and hidden spots. Break cleaner in a spray can is great stuff but be careful not to get it on your stock. It may dissolve the finish. Oh, use only the solvent based stuff not the water based one. The water based one does not do the job as well. Okay, that takes care of the spray brake cleaner question.
Someone may have told you that the brake solvent was good for cleaning your muzzleloader lock. Well, it appears to do a good job but when you disassemble your lock and wipe all of the hidden spots with a moist patch, you will find black stuff that the brake cleaner didn't get out.
To clean your lock, just dunk it into your bucket of hot soapy water and scrub it with a toohbrush. Then scald it with boiling water. Hold it with a pair of pliers when doing this. Immediately after scalding it, shake off any remaining water and spray with WD-40 to get rid of any residual water. Don't be stingy, WD-40 ain't all that expensive. Set it aside to drain and cool while you scrub and scald your barrel. Just as you did with the lock, immediately spray down the bore with WD-40 followed by dry patches to get out all of the WD-40. Then run a patch dampened with "Break Free CLP" through the bore and it is ready for reassembly and storage. Wipe your lock with a rag and treat it with some CLP, too.
These are the basic directions, there are details that I left out.
So, these are my thoughts on using Windex (works but too expensive), alcohol (works but too expensive) and spray brake cleaner (wonderful stuff for a quick clean of a lock but will never replace disassembly and washing with hot soapy water when it comes to a good cleaning).
Bottom line, nothing beats hot soapy water for cleaning a muzzleloader. It's cheap and it does the job.