I plan to use it to stream podcasts and music, hopefully that won't a lot a data.Oddly, I'm not seeing the data usage measurement in the EE app go down for my watch. I've definitely used data, albeit in low quantities as I have it for connectivity rather than streaming whilst running etc.
Do you plan to stream at all? If not, 10GB is plenty.
I couldn't find any up to date information on the EE website, is it still 10GB that comes with the plan?