I don’t have, nor have I used either tarp. But I have used an 8×10 flat tarp (similar to the split wing but no beak), a Pocket Tarp (similar to Descutes, but only one night of rain pre-addition of doors) and a Gossamer Gear One (which is shaped somewhat similar to the Deschutes but is a tent) and a Tarptent Squall (shaped similar to the split wing but is a tent).
In my opinion, tarps and tents that are shaped like pyramids are easier to get in and out of. When you sit up, your head goes pretty close to the highest part of the shelter, so you are less likely to get your head all wet. But it does depend on the overall size of the shelter, too.
Tarps and tents shaped like A-frames are easy to get in and out of if they are tall enough, but if they are not, it’s harder to get inside without getting your head or your back wet, or having to struggle in some way.
The Squall I borrowed drenched me because the doors in the front were like going through the car wash. When I sat up I had to scoot as close to the doors as possible to gain enough head room to sit upright. Anywhere else and my head would rub against the top and get wet. It was also very long and so almost half the shelter was useless to me because I could not reach down at the foot end without getting my head wet rubbing against the top. If the Split Wing is similar in size and shape, you might get annoyed.
My A-frame tarp was very nice to use in the rain. It made a large living space where I could keep my wet stuff away from my dry living space. I set it up tall which gave me lots of headroom and was easy to get in and out of. I set it up so the 10′ side made the ^ shape and the 8′ side was the ridgeline length. I experienced 6 days straight of rain and was comfortable and dry. If the Split Wing is similar in size, you will be comfortable.
My Gossamer Gear One makes a similar large living space because of the generous vestibule and the tall height. I can sit up easily without getting my head wet. The pyramid shape provides a lot of room. If the Deschutes is about the same size it would probably work just as well.
My Pocket Tarp, before I added doors, was easy to roll out into the rain. I have yet to see how it works with doors, but it should be an improvement. I doubt it will be as safely dry under there as my A-frame flat tarp is because the sleeping area is only about 30″ wide, maybe only 26″ wide. Being not spacious, it is hard to find a place to sit upright without my head rubbing against it. If the Deschutes is similar in size you might have similar issues. I’m only 5’3″ tall.