Twilio Video: native relay captioning vs. third-party captions via Functions for a group-room app

I'm building a customer-facing video support app on Twilio Video using group rooms, and I need to decide how to deliver real-time captions that satisfy WCAG 2.1 AA. Two documented paths seem viable: enabling Twilio's built-in Video Relay Captioning at the room level, or wiring a third-party captioning API through Twilio Functions so I control styling, latency, and fallback behavior.

My constraints: the captions must be styled to match our brand (font, contrast, positioning), we have a mix of short and hour-long sessions so per-minute third-party costs matter, and some callers join from older browsers where I can't easily verify how a custom caption track is rendered in the published media pipeline. The native service appears to offer only basic language selection with no styling control, while the custom route needs token parameters and webhook configuration on top of room setup.

Given these trade-offs:

• Can the native caption track's appearance be influenced at all from the client SDK, or is it fixed?
• For the Functions-based approach, what is the recommended way to embed the caption track so it survives track subscription changes mid-call?
• Is there a documented way to measure caption latency for either option before committing?