Rome Omnia Pass vs. Roma Pass

The Omnia is a rip-off, if not a plain scam. They buy a Roma Pass on the official site, then they buy a Vatican Museum ticket on the official Vatican's site. Then they put the Roma Pass and the ticket in a nice envelope and sell it to you for twice the prices of both.

No pass can include the Vatican's Museums entrance, it's a foreign museum that does not make agreements with Rome's tourism board. Saint Peter's Square and the Basilica are free, there is only a security line that nobody skips.

The way the Roma pass works is explained on their site: the first two attractions are free, from the third site onward you'll get tickets with a discount.

Here's a list of the Museums you can choose from with the Rome Pass. Tap the picture for more info.
https://www.romapass.it/en/museums/

List of full & 50% off prices for above Museums.
https://www.romapass.it/files/doc/SitiAderentiCostoBiglietti20191112_eng.pdf

To add to the above (and yes, the Omnia card is a ripoff), note that there are 2 versions of the Roma Pass: one good for 72 hours and includes free entrance to 2 attractions, and one good for 48 hours and includes entrance to just one attraction. As Dario said, other attractions covered under the pass are discounted (involve fees) during the 48 or 72 hour activity of the pass.

The Roma Pass doesn't include anything at the Vatican so you must buy tickets for that one separately. Here's the website:

http://www.museivaticani.va/content/museivaticani/en.html

Also note that with the Roma Pass - which also is part of the Omnia "bundle" - you must make a timed-entry reservation for the Colosseum: see the instructions under bullet point 7.1 on the FAQ page of the pass website:

https://www.romapass.it/en/FAQ/

Thank-you so much.... very helpful input!! :)