If you need a copy of your TM30 registration for a visit to the immigration office I definitely recommend you to ask the hotel before booking or paying any money.
It's true that all hotels should do it, but it's also true that many just don't do it.
If you want to extend your stay in Thailand go to the nearest immigration office where they will explain to you what tö do and even supply you with the necessary forms.
Many people are using these "tickets" and reporting enthusiastically that they didn't have a problem. Unfortunately they usually don't tell us whether they really were asked tö show that ticket at immigration or at the airport check in counter......
I don't use them, because there are other options which are not really much more expensive.