What are the differences between Kreg K4L Pocket Hole Jig (Model #K4L) vs. Kreg K4 Pocket Hole Jig Master System (Model #K4MS)?

From what I can see, just the accessories that it comes with. Some of the tools are over $20 so the extra equipment may be worth it, if you intend to use it heavily around the home or business. It offers a vise clamp set, an additional removal single drill guide for mobile use, a dust collection shroud to hook up to a vacuum and a couple smaller adapters. The regular system is fully operational and will perform equally as well as the master system. I would recommend the pocket hole vise clamp (not the model featured in the master set), as it has a blunt, pointed end that holds the two joints together to a perfect 90 degrees. However, the tool alone is $25 ("Kreg Right Angle Clamp" at Lowes.Com). This will alleviate the worry of trying to hold two large pieces of plywood together. The clamp can only be used on an exterior pocket hole, however, and not interior holes. I hope this answers your question.

the K#4L is just the jig, and the drill bit and driver, the K#4LMS (Master System) includes all in the K4l plus Clamp, dust protection fitting, pocket hole fillers, some screws, and a drill guide block