Both are important for the workcation option. London is a good embassy to apply from, as many posts show. If you have the financials and job you should be fine.
Anonymous participant Yes, you have to take the agent's word. You could contact the embassy directly to confirm your application was submitted. i guess but take note of James Miller reply. Baan Thai Solutions is among the more reputable agents but strictly speaking you need to be in the country of application.
I think DTV is far superior in terms of value for money. I find no hassle with the DTV, simply leave and re-enter get a 6-month stamp, rinse and repeat for 5 years or maybe more.