G'day again Mark.
It appears that you are looking at the Ace as well as the X-Terra 30. On paper, these 2 detectors are about as close as 2 detectors can be. they are both easy to use. Ive got a couple of hundred hours on each of these machines and enjoy using both of them. At the end of the day, it is going to come down to personal preference. About the only direct feature that one has that the other doesn't, is that the X-Terra has a volume control, which makes hunting without head phones, a more enjoyable experience. the Ace is easier to pinpoint with, but I've recently found that I've been able to adopt that technique to the X-Terra, which makes it easier to work with. To get the best pinpoint, you hit the pinpoint button and centre the coil over the target. you then pull it back towards yourself till you lose the target, then slide it back till you reacquire it. then just give the coil a bit of a wiggle as you draw it back towards yourself again.This will put the target just under the 12 o'clock position, under the inner coil. The X-Terra has a completely different sounding pinpoint to the Ace. With the Ace, you are listening to the audio fade, but with the X-Terra, you can listen to how loud it is over shallow targets. Screw caps tend to sound louder than coins.
The audio system on the X-Terra is easier on the ear than the Ace. Also, the recovery speed on the X-Terra's are a bit faster, which means that you will get better target separation if there is a lot of junk int the ground. Also, the numbers are easier to read than the notches on the Ace. But that is only a minor thing.
At the end of the day, it will come down to what you personally like.
Good luck with your decision.
Mick Evans.