[Non-mechanic Opinion] Drill/tap combos can be economical for manual hobbyists with infrequent, one-off jobs, but they're much easier to break than traditional taps (possibly due to the material that is removed to form the drill sections). I have used them successfully and also broken more than one. I've had a lot of stainless work lately and have finally gotten a decent policy of double drills and taps, but for a few holes or infrequent repairs these combination taps can get the job done with a little care and patience.