rest.bitcoin.com Tech Stack
The main reason why you should use all of our fork stacks is because we maintain and guarantee that all of the components will work well with the Regtest address format. Allowing you to test locally more easily.
The blue part is the node that you choose. The default node is Bitcoin unlimited and there is Bitcoin Cash node as an option as well.
The red part is an indexer. ElectrsCash is for indexing Bitcoin cash transactions and aggregate BCH balance per address. Without these, you won't be able to query the amount of BCH you own in a particular address. OpenSight is a shim micro service to make ElectrsCash compatible with rest.bitcoin.com API interface. SLPDB is an indexer for SLP token, color coin on top of Bitcoin Cash, this will be verified if the data relate to the color coin is valid and checks if the coin follows the SLP off-chain consensus.
Chris Troutner JS Tech Stack
The main difference is the rest interface. bch-api has a different API from rest.bitcoin.com and can talk directly to Electrscash without requiring the shim.