That style of vise is good for holding large and awkward shaped parts to the table, and it takes up zero headroom under the spindle, which can be useful. It does, however, also spring the table surface into a convex curve, which can affect the results of the shape of the finished part, and might make the warp permanent if you gronk down too much on the work...
That was a generic comment, your 22L is a pretty stiff and solid machine and probably won't know the difference.