I mean, at $17 from Sirius, not getting the right drill tool seems kind of penny wise pound foolish. If it saves you from one zipper or damaged chute from a mistimed delay... Heck, you can buy the tool and a reload from Wildman for basically the cost of one HAZMAT charge!
The other nice thing is that the aerotech drill works with all their rms loads from 18-38mm, so now that you've bit the AT bullet you can grab the very nice 24/40 case as well, which is a brilliant little motor, especially for Estes kits that are a bit wimpy on D12s (I've got a mean machine kit back from before they came with a longer engine mount to accommodate high thrust Es, and it flies beautifully on the E18 RMS).
One issue you'll have with the CTI drill is that I believe the RMS delay grain is quite a bit narrower than the CTI, and the drill bit on the CTI is also fatter. So you might have trouble drilling the grain without hitting the sides if you're even a little off-center, which might be bad news.