Sorcerer/Wizard spell selection I assume?
The BAB thing strikes me as suspect... but they get even less variety in spells than a Sorcerer and less spells per day so I guess it balances out.

If they end up with a lot of spells "At will" I could see it working in a large enough party with only up to 4th level spells... still would want to have a sorcerer or wizard in the party for the higher level stuff, but as a "I continua-buff everyone with Bulls Endurance" it might have a role... They might tend to become non-offensive or at least non-saving throw based in the long run without higher level spell slots to boost the CRs... also watch out for expensive material components if you are making it SLAs... there may also be other benefits to SLAs I am forgetting but...