Some things to think about when hunting "easements". Although it is legal to be on these pieces of dirt, they do belong to someone and you should be very respectful of that. After a few people come out and yell at you it will start feeling very creepy, but just be sure to leave the place you dug as near as possible to the way you found it and mostly you will be OK. It is probably best not to ague the law if you are challenged, just move on down the block. In some easements where it is clear people have spent a lot of effort to plant grass or plants it might be a good idea to skip over them. When the weather has been dry for awhile, digging a hole will leave a dead spot almost guaranteed, so try to dig when the ground is damp.
Having said all that, the easement is a fantastic place to find old coins and relics if the neighborhood is old. A consideration for which detector is best is that the easement has most likely been hunted before (it has been a good place to hunt for many years), so get the best detector you can afford to use on these places because the shallower items have mostly already been picked over and you will be looking for deep signals. In fact, because I try not to dig in the easements unless I am pretty sure it is something worth going after, I will only dig the deep signals. I use an E-trac now and because it seems to be about an inch deeper than the last generation of detectors I am finding a lot of deep missed coins right now.
Hope this helps