The ball at the back means they dont turn around, and are ideal when going xc as they arent very long, so the chances of stepping on them and falling are reduced. They are also very hardwearing and padded, and last a good few years! They also seem very reasonably priced.
Depends what u wanna use them for. For cross country i think the best ones are the pyrani(cant spell it) rubber ones that pull on the long 'neck' means they dont turn upwards like some. The velcro ones are useless after diving into water they more often than not get soggy and come undone.
Another vote for the Professional Choice ones or think Sportabrac or Equilibrium make a pair very similar for similar price with the heel stop in to stop them spinning. Would highly recommend.
the velcro does not come undone in the water (i have had the same pair for four years and never experienced this)
i have used them all the time (hunting, showjumping, cross country, hacking and scooling) they still come up like new.
they don't turn upside down, and they don't spin causing rubs.
i can't reccomend them enough. i got sick of my horse destroying her rubber ones and invested in these (well worth the money)