The decision
After-hours answering should follow the practice's own instructions for urgent and non-urgent messages. Agree the on-call contact, backup contact, handoff process and expected record of each interaction. Do not leave urgency decisions to an undefined generic script.
What to compare
Shared services may provide round-the-clock availability; a dedicated part-time assistant covers only the scheduled shift. Check the actual plan, holiday arrangements and whether time spent routing or documenting calls is billable.
Before you commit
Run a scheduled test of the escalation chain and update contact details whenever the rota changes. Make it clear that callers with emergencies should use the appropriate emergency route under your practice's approved instructions.