The older Fisher units,
First the 1236 is not a metered machine, but for all intent purposes the 1236 may be a littler deeper detector, but without ID.
I have an ID Edge, never owned an Excel. I'm going to say that the F2 would not do any better than a proper working Edge, and not likely will the F2 ID as well as the Edge does when things gets beyond 5 to 6" deep.
Remember, with the F2 your talking about a entry level $199.00 "New" an Edge used is bringing $250.00 The F2 is a nice little detector that has a lot going for it. But, your in a little different class in your comparison. (Oh, I also have owned an F2)
Now, how would the F2 compare to an,
ACE 250
Most Bounty Hunters from the mid price range down,
Most any other $200.00 detectors,
Probably superior!
Also, keep in mind that the Fisher F2 as with the other F series detectors they are made by First Texas, now I don't mean that as good or bad, but the older Fisher units were built by the original Fisher Company which First Texas acquired a few years ago.
Mark