We worked with Astrea on a small custom Lightning component and they were great! Their quoted prices are very reasonable, and they were communicative and helpful every step of the way.
We discovered some additional needs to make the component fit our workflows while testing their first delivered version of the package, and they were kind enough to make those tweaks very quickly (<24 hours) at no additional charge. They checked in and made sure everything was working the way we needed it, and answered my many questions quickly and thoroughly.
We did have to do significant testing/QA on our end--found a bug in their initial delivery--but the Astrea team jumped in and fixed anything I found very quickly, even if it was more of a 'need an additional workaround for Salesforce limitations' type of issue than a code bug. Overall, I can't recommend them highly enough. Review collected by and hosted on G2.com.