I use the slightly larger 4 gallon Solo sprayer with diaphragm pump and have found it to meet my needs.
My orchard spans about 22 trees, so similar to yours. The tip of the sprayer nozzle can become clogged with Surround, but it is easy to disassemble and rinse as there is a small filter hiding in there. I would recommend getting into the habit of cleaning the tank and sprayer tip after every use of Surround. Otherwise, you will notice yourself pumping the sprayer more frequently to get good flow.
The shoulder straps are somewhat clumsy and can come off easily, so you have to be careful when lifting the sprayer onto your back.
I got the Solo brand extension for the wand, and have found it to be essential to get complete spray coverage on semi-dwarfs.
For the price, you really can’t go wrong with this one.