Direct answer: why not? Everything is experience and experience is never bad. Unless there is some real alternative that would give you even more experience.
Being in such a role is lots of fun. Refer to @Paul answer to see that interesting things you may expect - these are true, these are difficult but assuming the minimal expected background, this just makes you better specialist.
Just do not expect to become a boss in this company in the future. Big bosses do not grow within the same company where they become the big bosses. They move between companies all over the world, gradually getting higher positions.
From experience, this may fork in the future in a few different ways:
- The company succeeds only moderately; they do not grow much and maybe
hire a few more developers without the need of the big hierarchy for
such a number of people. At least one additional developer is expected ASAP just to have a replacement if you are on vacation or leave this job. This is probably the best you can expect and this is really not bad.
- The company fails, you stay with a few years of interesting work
- The company succeeds and grows; the boss hires a supervisor with
blindingly great CV for you. First thing to do this supervisor
insists on complete rewrite of your software (does not matter it
works well and actually brought the success).
- If the company is very much into some other business than IT, sooner or later they may find a suitable off the shelf commercial replacement for homegrown software and switch into it. The risk of this very nasty turn depends on how much specialized and unusual the software is required to be.
However, you can always look for another position. And another. And one more, staying a year or two in every job. Working hard to learn technologies and relations between people.
Do not feel guilty for that. Not a problem. This is the way to become the big boss.