All antennas of this sort are compromises both in electrical and physical aspects. None of them will perform as well as a well designed, 'obtrusive', heavy duty, real 'full-sized' antenna. If that will satisfy your requirements then this sort of antenna should work for you. One part that isn't stressed in any of the advertisements is that a -good- ground system is required. That means that a couple of radials of about the 'right' lengths for a particular band is very, very seldom going to be very 'good'.
That 'performance' thingy is about radiation patterns, not about a nice SWR. World of difference there. Those radiation patterns are dependent on physical size/height. I'm afraid there's no way around that. So, if you expect fantastic performance on bands where the antenna isn't at least close to a 1/4 wave length, be prepared for disappointment. Happy thought, huh?
- 'Doc