All three use the same base plate with the 390 and Targa having additional milling to reduce weight. The big difference is the highback. The Arsenal has a shorter, wider and substantially stiffer highback. The 390 and Targa are a taller, narrower and very flexy highback.
I prefer the Arsenal for backcountry, freeride and off piste because of the added support and very simple,durable design. You don`t want a "wardrobe malfunction" in the backcountry. I find the 390 and Targa more forgiving for freestyle. The Arsenal is the ecconomy model with a no frills system that is comfortable and durable. Lots of adjustability as well as a toe strap that can be used conventionally over the toe or as a cap strap.
I think the 390 is the ideal park bindings in that it is light, responsive, yet forgiving. It has better padding that the Arsenal and is slightly lighter. The Targa is the premium binding with the same performance characteristics of the 390, but with a lot of extra features. It weighs slightly more than the other twon and is the most expensive.
I have the Arsenals and 390`s on my boards and love the hell out of them. At first, I found them a bit touchy compared to lower end bindings and had a tendency to oversteer. Once you get the touch dialed in these things reduce your workload of controlling your board greatly.
There are a lot of great bindings out there on the market and these hold the honor of being in the top 10 in my book.
I considered the Rome 390s before, but ultimately went with Burton P1 Wingtips because overall I liked the design. The P1's are very forgiving, padded base with extra cushioning and they definitely felt good in the park last night.