Question #1 - Duo-Fast. They have a lifetime warranty. They will fix it at no cost. All guns will break at some time. Question #2 - Yes, the list is many. Question #3 - All nails (even Duo-Fast) will not fit all guns (even Duo-Fast). On BIG projects the cost of nails (Duo-Fast or generic for the specific gun) are expensive , but one makes that up in labor saving costs. For small projects it may not be worth the expense. Example, I will never roof a house again without a nailer. A dog house....50 cents worth of 16d box nails will get the job done.