Sounds like you are going to like the F70. I was very interested in reading your post because I have recently begun using the F70 also. I have had mine for about three weeks, have about 25 hours on it. It came with the F75 coil. It is definitely a nickel getter, 31 or 32 are strong nickel numbers for me. So far, besides some clad, I have found a '64 rosie, a '66 Canadian dime ( 80% silver), and two silver rings. One ring was quite small, the other was a chunky MEX band type ring. It gave me a beautiful 90, 91 signal, very stable numbers ( for a change ). I thought I might be over a clad half because it wasn't deep, about 2 inches. It was a nice surprise to see the silver ring. The light weight and long battery life of the F70 are very nice and it is also very nice to have some very knowledgeable mentors to help us along our journey. Thanks you guys very much !
Here's a tip for you. My last time out with the F70, I dug four very iffy targets. Crappy audio, different numbers flashing on the screen. I thought about passing them by, but I saw my nickel numbers 31, 32, flash on the screen and decided to check it out. Three out of four times it was a nickel ! Fourth time was a pulltab. I thought that was very impressive !
I was also very interested in your comments about the CZ7a Pro. Or maybe I should say I was a little confused and bewildered. Our winter here in the Northwest was mild ( sorry guys ), so I was hunting a few times in January and a lot in Feb. March and April. I was primarily using my new to me CZ7aPro. Since I only notched out iron, I was hearing everything else, which is what I wanted because I was hoping to find some gold jewelry. I did end up finding a nice 14k ring with diamonds, and I was finding nickels, a lot of nickels. Most of my time was spent at three sports fields that are close to my house. When I saw you post about your results with the CZ7aPro, I couldn't hardly believe it. Only 3 or 4 nickels in a whole year ? So I counted my nickels and I am at 171 so far for 2015. 36 were found with my F70, 16 with my CZ3d which I used about 5 times, and all the rest were found with the CZ7a Pro (119 nickels). I was very impressed with how often it said I was over a nickel and that's what it was. Yes, it was fooled once in a while by a pulltab or part of a pulltab and many times by those pesky metal bands around pencil erasers. But several times I smiled and chuckled and said to myself, this CZ7aPro is great at finding the nickels ! .
I think the F70 might be a better nickel getter than the CZ7aPro. They both seem to do a good job. I am liking the 3H tones for now, nice to have that high tone alert for nickels. Good luck to you and your brother with that nickel competition !