AK with an underfolder stock:
Basically any AK side optic mount will fit the AK Master Mount TM side rail. The two main styles of optic side mounts are classified as the "regular styled AK side mount" and the "SVD styled side mounts (these have the central rotating cam that fits into the scalloped out area in the center of the dove tail part of the side rail)." Both styles fit the AK Master Mount TM side rail. Which ever mount you choose will only require the initial adjustment of the locking bar to fit the dovetail on the side rail. You can then remove the mount and replace it without further adjustments.
It is purely personal choice which brand or type of optic mount to choose. There are many commercially available optic mounts available at different price ranges. They all have their pros and cons so it really comes down to personal choice which brand on type of optic mount to choose.
My recommendation of how to place the AK Master Mount TM side rail: Use a small punch or long nail to follow your factory axis pins out of the receiver from right to left. This keeps your trigger and hammer assemblies in place so you don't have to fight the springs. Then place the female end of my long bolts over the tip of the punch / nail and follow it back thru the receiver from left to right. Once again this keeps the hammer and trigger assemblies in place. Align the octagon head of my proprietary bolt in the corresponding cut-out in my rail and secure the bolt loosely with my short screw. Do one pin at a time.
After removing the dust cover and the axis pin's shephards crook retaining wire, remove tension from the hammer spring to facilitate axis pin removal (and to avoid hammer spring "bite" to your hand). This is best done by pulling up the two wings of the braided wire hammer spring and securing the wings behind the hammer head with a bread wrapper twist tie.
My thoughts on the included lock washers: I recommend using the included locking washer on the initial installation instead of thread locking compound. This allows you to make sure you are happy with fit, function, etc., and not have to break loose thread locking compound if you are not. This also allows for a trial period to ensure the proper amount of tension is applied to my pins as the AK Master Mount TM side rail is held to the AK receiver wall by compression. The recommended torque on the two short Allen head screws is 7 lbf/in. After several shooting sessions, then remove the lock washers and place thread locking compound to resist the vibrational loosening forces.
Optic Mount Choice:
Any side rail can be problematic for an underfolder AK as the underfolding stock may hit the side rail when the stock is folded. The inside of the folder arm is usually notched (like is done to clear the safety lever) to allow it to fully clear the side rail. Regardless of that, the optic mount will definitely have to be removed from the side rail in order for the stock to fold up. This is true for any brand of side rail.