Bat is one of the better and most universal devotions in the game. It’s especially good on casters without WD skills to sustain. Plus red/green affinity is usually needed.
Turtle is nice on casters with CDR and other forms of absorb, but is far from great. Sometimes it fits in your devotion route. Here’s my Reaper with both Turtle and Bat. [1.1.4.0] The Undead Shinobi of Cairn - PB Reaper, Gladiator in ~ 6 minutes