How does it work in incessant rain?
Pretty well. Actually as long as it isn't grounded out on too much grass, it's all good. Drought is actually worse as it can cause conduction issues in the grounding rod(s). Ice in winter will weigh it down and ground it out. With a half inch of ice mine bent almost completely over to the ground. Fortunatly it wasn't in use, I just didn't get it out before the ground froze. But once the ice melted, they popped back up. only one post was bent a little.
Different kind of energizer specs?
With more juice you can run more
fence or overcome a heavier weed load. If you wan to expand in the future you won't have to buy a new charger if you get something with some extra power now.
Double spike of single spike?
I like the double spike. I think it's more stable and you can work it around a bit more to get the right angle without loosening the hole too much that the post falls over. If the ground is really rocky the double spike can be harder to get in the ground. It's also harder on frozen. frosty ground with two spikes.
Integral posts or otherwise?
I like the shorter lengths of
fence because they are easier to move. The closer the posts are to each other along the fence, the easier it is to deal with, especially on uneven ground. If you need to put posts in between, use a good wooden stake and tie it. The plastic extra posts are kinda weak and they tend to bend especially in direct sunlight. They get soft when they get hot and they tend to stay that way.
Height with or without wing clipping?
Think of the fence as a deterrent and not a barrier. Almost any
chicken could get over if it really wanted to, most choose to stay in because the deal is better in the fence. Some birds are repeat offenders and I would say to clip one wing. It puts them off balance. Don't put anything they can jump onto near the fence. They will use it as a launch pad to get over. That being said, taller fence is better as a deterrent. Also, heavier breeds are more likely to stay put.
Uneven terrain?
It depends on how uneven. I live on a hillside such that a
chicken on the high side of that paddock could go airborn and glide over the fence on the low side of the paddock. It happens from time to time when the get too excited they go back in with a bribe of food. If you mean lumpy ground, I would suggest clipping the bottom horizontal wires so that they don't ground out on the lumps when the bottom of the fence touches the lumps.
Are there different grades of fencing out there?
I like the premier1 brand but I haven't tried the others. Most other people I've come across seem to like the premier1 stuff too.
Best wishes