This x 1000!
For the past decade, I’ve been renting farms. As I renter, I haven’t been able to make permanent changes to fence lines (nor have I wanted to pay to do so on someone else’s property), so I’ve always used step-in posts when I need to section off something. I use them with both electric tape and wire.
The plastic ones in the top link are garbage-- the slats to hold the tape/wire snap off easily, the posts bend and bow with the tiniest amount of pressure, and worst of all, I’ve had them snap in half after only a few months use, leaving jagged plastic exposed.
While I hate fiberglass, I have been pleasantly surprised by the ones in the bottom link. I bought a ton of them in a pinch back in 2012, and even after 8 years in the elements, they are in good shape. My only criticisms are that they are very short. Also, if your soil is exceptionally hard or rocky, you’ll likely have trouble getting them in the ground. The risks of fiberglass are always in the back of my mind, but knock on wood, no issues…