I haven't used this coil, but if I did have one, I would only use it in trashy areas.
They do also say, this is the coil to use on wet sand, where it works well.
I use the Ace 250 and bought a Sniper coil. I could throw the original coil away. I only use the sniper now. Seems to go just as deep and is so much more easy to pin point with. Get one, you will love it.
I have read some good reviews of it here http://www.thetreasuredepot.com/cgi-bin/garrett/garrett_config.pl?#24716 plus what chugs said.
I'm thinking about getting me one, I guess the price is not too bad as far as coils go, but seems a bit steep, nearly a third of what the machine with stock coil costs.
The sniper is for more trashy areas to get away from bad targets masking good ones. It will also allow you to get closer to metal fences, play ground equipment etc without giving off a signal. It's one more tool to have in your metal detector tool box. As for the Crossfire coil they will work. In fact most Garrett coils will work with the Ace machines but your target ID and depth readings on the meter will be off.
I used my 4 " coil for the first time thursday because
the area had tons of trash. I kept digging up junk even though i knew because the meter was jumping. I was getting discouraged after 1 hr under a hot texas sun.
As i was wrapping it up i hit a solid nickel on the meter.
It wasnt jumping so i thought i would dig. After digging about 2 almost 3 inches i found a nice gold ring. Not too fancy but gold. i think 10 kt. I had never used coil before and i thought , I am glad I bought it. Alot of trash here. i havent hunted anymore , so i will keep it
on. I have only had my ACE250 one month and I am getting to know it better. GREAT MACHINE AND COIL.
I hope this helps.