I have a Giottos MH1300 Tripod Head with an Arca (somewhat) Compatible Clamp. When I mention, "somewhat", that qualification results from the safety stud which would prevent a mounting plate from slipping out of the clamp if the clamp is not correctly and securely tightened. A Giottos clamp will slide straight in from the rear because there is a channel cut into the bottom of the Giottos Arca Plate that facilitates the plate sliding into place. Pressing the red release button at the rear of the clamp will allow the plate to be removed. The release button, when pressed pushes the button over to the channel cut into the plate.
I had a problem when I tried using other than Giottos Plates on the Giottos clamp because the safety stud would not allow the plate to slip into the groove. This happens with both standard plates as well as with L Brackets. However, I got around that by opening the clamp fully and dropping the plate in from the top. A bit slow but, it works fine both with standard Arca clamps and with RRS L Brackets.
Now I have a 100-400mm f/4.5-5.6L IS II lens on which I installed a Kirk Foot. The Kirk foot (which is Arca Compatible) is far more secure than using the OEM foot and attaching an Arca Compatible Plate to the foot. That is just one more piece of gear to fail.
The problem with the Kirk Foot and the Giotto Clamp is that these are not compatible and I can't seem to fasten the foot onto the clamp at all, due to the above mentioned safety stud. I had one of two choices: Removing the stud or purchasing a new clamp to fit on my Giottos head. I have not had that problem using the Kirk Monopod Swivel Clamp.
Since the only plate that the safety stud works with is the original Giottos plate that came with the clamp. I have removed the safety stud. Luckily, this is done easily with a small Allen wrench. Looking down at the stud, it didn't look like it was slotted for an Allen wrench. However, I noticed that it was when I viewed the illustration posted above. The Foot fits just fine now and I don't have to open the clamp entirely to mount or remove other plates. Loosening the clamp a bit and sliding in the plate from the rear works just fine.
I just need to keep any plate securely tightened into the clamp.
Actually, the Giottos ball head is quite nice. Like many expensive ball heads, it has three control knobs. One knob controls rotation, one releases pressure on the ball and the third adjusts the play of the ball when the pressure knob is released. The head is quite secure when finger tightened.
Additionally, using an L Bracket is a great way to work with a tripod and ball head. The camera doesn't need to be cantilevered over on its side for a vertical shot so the head doesn't need to be secured quite as tightly.