The module keeps price history both automatically and manually. Precisely in 3 ways

1. Automated cron jobs 

2. Manual one click sync for old or new price

3. Automated with hook (When the price is updated or discount is added)

Automated with hook sync is when the price history sync on product update or discount created or updated.

Yes. You can stop history sync from settings untill your campaign ends. 

Yes, price history chart is available with vast customisable features

Yes, With the manual one click sync you can put single product is or range of ids to sync only the products you need

Eu Omnibus Directive the new legislation designed to protect consumer rights in the European Union mostly for the eCommerce sites. As per the law the eCommerce sites are required to show the lowest price within 30 days to keep the pricing transparent to the customers during discount campaigns. 

Also the retailers must show if the pricing shown to you is based on personalized data or other source.

Omnibus Directive Law also improvise maintaining authentic reviews for the products of the eCommerce so that the consumers know that the published reviews are from actual customers.