Ventajas
Flexibility is the only pro. (That and meaningful work/great colleagues--this is how they get you.)
They do offer part time positions, but benefit costs are ratcheted up to double and quadruple what full-time workers pay--and yet it seems the majority of posts are mandatory part time, despite branches needing help. When one branch was insanely understaffed for more than a year during the pandemic, several interviewed, vetted candidates turned down positions because they would only offer them part time hours & unaffordable benefit payments. (ACA costs less, but you can't get it while working there...)
Another pro: running across books like "Work Wont' Love you Back" that detail the exploitative nature of the non-profit sector and 'prestige' jobs like libraries, teaching, nursing, and how they weaponize our desire to serve. SIGH.
Desventajas
If it's not, it should be illegal to pay on-call employees the same hourly rate (with NO real benefits) as regular employees. This means 30-40% LESS compensation for trained, experienced, vetted employees who show up to keep branches open. Nobody, including the union, wants to talk about it. "Its better than it was." doesn't mean it's not still exploitative. $1.50 an hr "in lieu of benefits" and some sick leave. One can be on a long-term temporary posting at a branch--showing up and being an integral part of the team-- and be the only person going unpaid for major holidays. In what universe is that equitable?
Also, major lack of transparency around benefits and options. You have to ask, and you have to be specific, or you have to comb through a messy, ambiguous contract. These things should simply be clearly posted.
Lack of respect, fair benefits policies, transparency, appreciation and opportunities to move up make this a dead-end job or just a stopping place.