I've split 10 gallons in two, three and even four parts, but ultimately the choice is up to you. Splitting in four parts isn't something I'd recommend unless you have several very laid back fish, as the two in the middle will have a fish to bicker with on both sides. That or have female fish in the two middle sections, and males on the outer sections, I'm going out on a limb here (I don't keep females myself yet) in that the females will tolerate seeing another female than some males will. Also, if you split in four, you will probably want to silicone the dividers in place, as the spaces the fish have will be narrower, and some especially feisty bettas are in fact capable of pushing the dividers if they aren't secured. They can push the divider over onto the next fish and trap them in a tiny little section with one divider on top of the other if you aren't careful.
An important thing to bear in mind when splitting a tank is who is going to be next to who, and whether or not they will tolerate each other's presence.It may take a little shuffling to get them all settled in. If you split a 10 gallon three ways, put the least aggressive male in the center, or if you have a female, stick her in the center, it will help diffuse the male's aggression, and turn it into courting.
Males (at least in my experience) tend to be least aggressive towards each other when housed in a 10 gallon split 2 ways, I suppose it is simply because that give them more room to get away from seeing the other male betta if they want.
Having spare tanks for putting single fish in is always nice if you have the room, because sometimes you will just end up with a fish that will not get along with anyone.
I'm assuming the male you are getting from Aquabid has been housed next to other males his whole life though (there were other males next to him in the pictures), so he should be somewhat used to being able to see other males, and should be able to tolerate being in a split tank fairly well. But again, it's always best to observe these things closely the first couple days to make sure.