As soon as I saw a 4-wheeled Polaris, I thought it was an excellent alternative to the goblin for those that didn't want to build a full car.
I'm disappointed in how expensive the conversion kit is though. They vary based on brand, but the cheaper ones I've found are in the $7k range. So now you need a slingshot (looks like about $25k), plus a conversion kit, and then you have a NA ecotec that's heavier than a goblin and costs a lot more.
They still look cool though. Maybe DF could design a 4 wheel kit for cheaper? It's just some tube steel control arms, some shocks, hubs, and a donor rear diff. Seems right in line with the stuff DF does.