hehe - actually I am an Android dev primarily and I thought that starting a project without CI sucks way more. So I built this for myself and was happy paying $7/mo for not having to spend weeks+$$$ on setting one up with current solutions.
Spot instances do take upto ~2 mins to come up so probably a turbo add-on that devs will feel happy paying for or please feel free to suggest.
Yeah, if there's no space for an extended period of time the service will be useless, with an endless backlog of jobs.