I wouldn't be worried about the water pump or sensors clogging upI've not had any problems with the KSeal I've fitted the new thermostat as previously mentioned and bled the system since using it and every thing is working fine. I take your point though, but if you Google it it's a lot better than it used to be eg more refind for todays applications and its sold all over the world. It does state on the bottle that after putting it in and the leak has stopped you can drain the system and re fill with the correct coolant mix.
The GM factory service manual for the Grand Am late 90s recommended add the GM sealant tablets with every coolant change
Can you still buy them they were like £2 back then, I can't remember the name now, they were made for GM by Barr I think
KSeal is pushed mainly at motor trade professionals and have sold over 10 million with very few bad reports.