I went with the kuryakyn horizontal mount. It mounts to the swingarm and is lighted. I like it. I think that a side mount plate looks great on just about any bike because it really cleans up the rear fender.
No need to buy one. Bend a piece of metal, drill some holes, use some LED lights, good to go! (Course I spent a bunch of money on a backing plate and a fancy plate bracket with lights. Wish I'd have taken my own guidance!)
Definitely with the build your own. Took a piece of sheet metal and an L bracket. Popped a couple bolts in to hold it in place. Use a hold saw on the L bracket and mount to the axle. The wire up whatever lights you want. I went with a $10 tractor tail light. Works great, looks good too. Total cost...less than $15