First, glad to see that you went from TwinJets to Jets.
I have Halcyon spring heels and have put two pairs on--a set for me and a set for my girlfriend on her jets.
With my jets I was at school in the dorms and had no access to a Dremel, but I did have my pocketknife with a file--so I spent ~1.5 hours grinding (by hand) the mushroomed piece of metal off of the pins so that I could put the spring straps on. Let's just say that my hands were very red and didn't feel so hot afterwards. Took forever, but I tink it was worth it.
When I put the spring straps on my girlfriend's jets I was a little smarter and used the dremel. I just ground off the mushroomed piece, popped the part off the pin with a screwdriver, and bent the metal retaining piece off with a pair of pliers. Took perhaps 15 minutes total--that included setup time if I recall.
If they're good quality spring straps you'll never need the old metal retaining system ever again, so don't worry about bending it.
A quick note on sizing--Halcyon makes an 8" and a 10" version. The 10" version is perfectly sized for me, but is too large for my girlfriend's feet. Unfortunently the 8" version is too tight for her. If they made a 9" version it would be great. We ended up buying the 8" version for her since too tight is better than too loose. After a week or two of class we eventually got smart and hung the fins from the door of her room with some weights in the foot pockets to stretch out the springs, and "now they fit perfectly."