After the trial ends, your ARM instance will get deleted and you will be back to free tier offer. You can use 300$ to try with. You have to upgrade to paying a

After the trial ends, your ARM instance will get deleted and you will be back to free tier offer. You can use 300$ to try with. You have to upgrade to paying accounr manually so you are not going to have surprise bill if you stick to free tier always and never upgrades. But good luck finding arm instance in your home zone because the demand is very high so you have to keep trying from time to time. There are some people using scripts to automate the instance availability and registration so they can catch the opportunity.