Excellent. Because those guides don't do much better than free hand with a square or something standing nerby for visual reference. On one of my cordless drills, I did the following:
Clamped a straight steel rod in the vice and monkeyed with it till it was stright per a level. Attached the drill. Put a blob of builders adhesive on the back which is now facing the ceiling. Pressed a small bubble level into the adhesive and adjusted for center. I have a couple drills that come with this feature but, they are corded. Using the bubble I can easily get as accurate as with one of those guides. Tried several, all lacking.
Any sufficiently advanced technology is indistinguishable from magic.
- Arthur C. Clarke