Every business is unique. There’s no one single best way to tell your clients that you’re not going to be around for the next few days (weeks or months). But there’s also no denying that whatever out of office message you use right now, you could always improve it.
Meanwhile, I do sometimes put up long ones when I will be away for some days during a season in which there are a confluence of three or four very likely reasons someone would contact me, and who else they need to contact isn’t the same. Like, it’s high llama grooming season, and generally during this month I get two or three requests per week for each of llama bleaching (for which my backup is Stella), llama shaving (for which it’s Arturo), and llama perming (for which it’s Carter). My message says I’ll be out until blah blah, and if it’s not an urgent llama grooming issue, I’ll get back to you after that, but meanwhile, for urgent llama grooming here’s who to call.

I apologise for this blunt email, yet feel I must warn customers and shareholders to divest yourself of any interests you hold in this company as the **** is about to hit the fan.
I say “I am out of the office without access to email” to avoid the expectation that I’ll check on vacation. With a contact for anything urgent given.