cool! I assume that is for electric fence?? the idea to make them removeable is excellent. Otherwise if the posts were broken your concrete would be wasted. I bet they are more stable and durable than those step in electric fence posts. I have used those before and they work but are real flimsy and warp easily.
Years ago I made some similar things. Took cheap aluminum cooking trays, filled with concrete with a PVC tee in the middle. Yours look simpler and cheaper. Good job.
That looks like a good idea. I think I might just put them in their permanent locations -- you could move the fence, but not have to be shifting heavy chunks of cement.
Another option for really hard or frozen ground, and it might be easier....just carry around an old fashioned hand crank drill (a brace, not the eggbeater style) with a 3/8 masonry drill bit in it...it's pretty quick to drill a hole in hard frozen ground or hardpan and the posts set nice and solid, and if you have a lot of ground to cover you don't have to carry concrete stuff around.
One drawback...in wet areas when you get a bunch of freeze / thaw cycles you can end up with some posts 'permanently' frozen in until spring...sometimes 'sproinging' them like one of those door stopper springs will vibrate them loose...