I've always liked my OBG type grapple. Unless your are just moving brush, the open flat bottom style just is more versatile. Better for digging out roots and small stumps. Better for loading more logs at once. Lighter and requires only one hydraulic cylinder and smaller upper grapple arm so is both cheaper and lighter so has higher net load weight capacity.
OBG style grapples do fine with brush but that is where the clamshell type does excel.
It is useful to focus on the implications of the different geometry. The RBG/clamshell type has a relatively vertical bottom tine orientation so for anything to stay in the grapple, the upper arm must be clamped shut. The OBG style doesn't even need the upper arm to load or carry a big rock or log as gravity will hold the load in place. The upper arm on the OBG is really just to stabilize the load so it doesn't need to be as heavy or wide. The RBG can only carry one log at a time usually as anything below the pinch point will simply fall back to ground. You can cram as many logs into an OBG style as you can fit and gravity will hold them along with light pressure from the upper grapple arm.
Because of the vertical "bottom" tines with the RBG, there is not much steel you can get under a root or rootball and not much leverage either. On the other hand, the RBG opens wider and when "dumped" open it can rake up a larger amount of smaller debris.
A
M59 has a powerful loader but unless you are using it commercially or allowing gorillas to operate it, there is no reason for a heavy duty grapple. Grapple names relate to skid steer use and virtually nobody with a CUT or even a
M59 will put the sort of stress on a grapple that a big skidsteer will. Light or medium/standard duty grapples would be fine on a
M59. I have a 300lb light duty 48" grapple on my DK40 which has done fine over half a dozen years of land clearing. At least one guy here on TBN has the identical grapple on his
M59 and has never complained. There are a number of companies selling these light or medium duty OBG type grapples and they clearly offer the best bang for the buck.
Width is another consideration. RBG types are usually five or six feet wide and seven is available though very pricy. Many of us have 4 foot ObG types and find no benefit to anything wider. Width doesn't add a lot of capacity to OBG types as a four foot grapple can carry exactly the same number of logs as a six foot grapple. The four footer is more maneuverable, easier to manipulate when digging stumps, and lighter so actually has a higher net lift capacity than any other grapple.
Basically, it helps to know what the range of tasks the grapple will be used for. Simply moving cut brush or split firewood or cleaning up a construction site is the strength of the RBG. Digging, stumping, log movement, digging out bushes are all relative strengths of the OBG type. Both types do very well with brush. RbG is fine as brush is compressible so doesn't have the pinch point problem that log transport presents. A OBG does well with brush even without the larger width or wider upper grapple arm because brush is "sticky" and it is easy to cram a whole lot of it into the open maw and then clamp it. OBG grapples are considerably less expensive and lighter weight.
Bottom line, if you clearly need the special capabilities of the RBG then get one. Most CUT grapple tasks are easily done with the more economical OBG however. And, don't make the mistake of thinking your grapple should be the same width as your standard bucket. Finally, don't listen to grapple manufacturers or dealers on sizing. They size for skidsteers and nearly always exaggerate the size needed for a non commercial CUT.
