These are also two distinct different products. It's the same content, but treated very differently. WotC's offering is a hardback book, to be read in a traditional referential way. Roll20 took the Volo's content and wiki-fied every single monster entry and lore page for the 5th Edition SRD Compendium. It's been automated so you can drag and drop creatures into your game with journal characters sheets automatically added, filled and tokens automatically linked and statted. The battlemaps of the beast lairs have their own module and have dynamic lighting already drawn as well. You can read up on the Roll20 version here: <a href="https://wiki.roll20.net/Volo%27s_Guide_to_Monsters" rel="nofollow">https://wiki.roll20.net/Volo%27s_Guide_to_Monsters</a>
