I bought the new SE Pro coil at Christmas for my Explorer II. It's about 5 - 6 ounces lighter than the II's standard coil.
It's much more stable than the old coil and you can usually run higher sensitivity settings.
Has better trash separation.
Seems more sensitive on small objects.
And you will notice the difference in the weight, especially on a long day of hunting.
Only downfalls I've seen are that it's cover really doesn't wrap high on the sides like most coil covers. I've cracked a few covers on the sides before detecting in the cold, around trees or rocks and would hate to crack my new coil.
Also the cross bracing is hollow / open on the bottom. Can build up with mud. I filled mine with black RTV silicone. Seems to work well. Can always remove or reapply it if needed.
Jeff