Selecting an Alko type stabiliser

I recently purchased a 1997 Avondale Mayfly, fitted with the old type lift handle and blade type stabiliser. On taking it for its first run today i noted that the blade kept popping out of its position on the caravan towing bracket. Is this likely because i fitted it wrongly- although i can't see where i went wrong. Should i decide to swap the towing hitch to an Alko type to get rid of this issue, what is the best type for a 2 berth Mayfly? is it worth the costs swapping? Advice welcome. Thanks'. Mark