Before that you must understand what is Systematic tripods first. Systematic tripods does not mean a lack of center column, my non-systematic tripod can remove the center column for usage too, but it is not systematic. And systematic can have center column as well. System tripods means a modular system where you can either have center column, or change the center plate to a leveling plate for video work or detailed panoramic work. In other words, a dual or multi purpose tripod. If you need or see possible needs in future, go ahead. Otherwise you can save some money with a more basic model.
With birding, always good to go with the taller model because you are shooting upwards most of the time. The weight difference is not a lot anyway and what is $20 when you are already spending $700.
Also, you may not need a ballhead. You can use your gimbal for landscape shots too.