Note as Cannon Fodder has pointed out, they are 'Spyder based' rather than being a 'Spyder clone', so the basic design is fairly standard 'Spyder' style, but there are a number of custom parts and they can be pretty tricky and tempermental.
Armotech is also a name to look out for, with many models being either Armotech or Warsensor.
The UK expert on them used to be Daniel Reid. I first met him & Skeletor many years ago at NvS in the days when he spent hi spare time at work machining replacement parts to fix the standard parts for Armotechs & Warsensors.
Skeletor gradualy tempted him out of the woods into tournament play