I also use the classic tag punch, but with the IV3000 sheets (#4007, 1-hand, 2 3/8 X 2 3/4 inch size) instead of tegaderm or opsite. About $32 for 100 sheets, $6 for 10.
After punching out the center for the transmitter, I remove just half of the backing, and stick it on. Then can easily remove the second half, and it stays in place and easy to tack down. Last, remove the top layer The only downside is that the IV3000 is slightly smaller than the dexcom white oval adhesive tape, so there is not complete coverage. But I prefer the smaller size.
Before applying, I apply skin-tac to the white tape around the sensor, overlapping to skin on the edges, then let it dry. Been using the same bottle for over 4 years and still half full.
The DexTape looks interesting, and may be slightly easier, but I will 'stick' with what I'm using.