How much digging are you going to do. If your setting a fence line for livestock then your also going to be doing a lot of fence mending. Some members love them because there cheap and will do the job under the right conditions for a little while. I have set a lot of fence in my day and most of it by hand. I personally own a Landpride PHD-15 that will mount to a BX as well.
If you ever set a lot of fence line you would understand the value of a good quality PHD. You get what you pay for in this world, my feeling is if it has a gear box buy a brand name but thats me. I think I paid around $1100 for my PHD almost 4 times what a your thinking. Some members think they are a useless tool, some love them, It really depends o how much experience you have digging post holes, It's more than just drilling a hole into the ground.
In addition to a PHD you also need a Spade, Clamshell, at least 1 Bar I have 5 different tipped bars, & a Tamper {pick handle works great} Depending on where you live there is much under the ground. You will have to cut roots 30 inches down in the hole, the tiny stone that turns into bolder sticking in the side of your hole. Your also going to have to clean out the bottom of the hole as well as occasional shave the side of a hole so your post sits right. For every 3 holes you dig in 15 minutes 1 will make you work for it and can take you a couple of hours. Drilling into Mother Earth is a little more involved than drilling into a piece of Pine.
Bottom line is consider your needs & buy or rent accordingly. If your just doing a 1 time short fence line I would just do it by hand or rent but if your have Livestock buy a good quality PHD