I'm a Software Developer by profession, someone who values the quality of work and prefers writing good code rather than fast code. I was working with a product startup for a year with great colleagues and I got to learn a lot in this period. The work was a bit hectic, but I loved it. A month ago, I quit the job to join a medium scale service company. Reason for the change was a bit of unstable conditions at the startup.
After joining the new company, I realized that the work here is not of my type, and the people here just write code to meet a business requirement, without thinking much about quality and maintainability. I'm not able to fit myself in the environment here, so I contacted my previous employer and talked regarding this. My previous employer understood my condition and has offered me the same position which I left. I feel that I'll be happy to accept it and continue working there again. I have two main points on which I need advice.
I fear that how this thing will effect my future employments, how will it look on my resume. How bad will this effect me professionally?
What reason should I tell to my current employer while resigning?
TL;DR: Is it professionally acceptable to return to your previous employer because of less job satisfaction at the new job, after serving a month? What possible reasons can I convey while quitting the new job?