Start with the model, not the hardware.
If a hosted service already runs a suitable model, your application can call its API. The provider handles its compute. You still need to account for your own application runtime, data storage and model-usage charges.
When a managed endpoint makes sense.
A managed endpoint can let you choose a model and deployment configuration while the service takes on parts of the serving infrastructure. You still choose access, capacity and scaling settings. Check what the service actually operates and what remains your responsibility.
When to consider your own runtime.
A GPU instance can be useful when you need compatible software, custom weights or deployment control that a managed service does not offer. That control also brings responsibility for updates, security, monitoring and recovery.