Yes, there is some overlap, but note that the monsters in the Monster Manual are more complete than the SRD ones. For example, Dragons in the SRD do not have lair actions. Just looking at the Table of Contents for each monster, you can see the difference: The Monster Manual contains the full text of the physical Monster Manual, in addition to tokens and artwork for all the monsters. The Tokens will look like the ones for the SRD (I believe they were backported from the Monster Manual as they didn't originally exist). Note that because the Monster Manual is a Compendium expansion and is tied to an Account, not a Game, there isn't a good way for someone to "share" it with you to check it out. But if you've used the SRD monsters (and it sounds like you have), it's identical in functionality, but with the full details of the Monster Manual (you can flip through it in a hobby store, or look at pictures online, or videos). Further, Roll20 has a great return policy, so if you buy it, look through it, and find you don't want it after all, you can email them at <a href="mailto:team@roll20.net" rel="nofollow">team@roll20.net</a> to see about a refund. (Feel free to email them first and make sure of that, of course).