Both are functionally similar and claim a 2.16% house edge with a 10,000 max win potential. Tome of Life is considered high volatility, while Scarab is medium volatility.
Tome of Life allows you to buy bonuses for 37x your bet amount (much less than the typical 100x most third party slots require), whereas Scarab you have to spin into them.
Both of them let you accumulate many additional free spins up to 180 in a session, but getting more than 3 scatters doesn't increase the base free spin count (only the play reward for the scatter symbols themselves).
I've had more luck on Scarab but sometimes it just eats.