We usually recommend to get a hair cut after three weeks. This is to make sure the recipient area and the donor areas are healed and there is no scabs left to make sure there is no risk of infection. After it is healed it is pretty much safe to get a hair cut.
Yes, you can use clippers but be sure that they are sharp, don't pull, don't dig them into your scalp, and they are clean. Many barber shops never clean them from person to person. Get someone who knows what they are doing.
Using clippers at one month is not a problem. Double check with your surgeon and their typical post op instructions.
Grafts are typically healed at one month post-op. Using clippers at this point should have no effect on graft survival.
Day 4 is usually the earliest one would recommend getting a haircut after FUE. Most doctors agree that everything is safe at a week post-op. You are a MONTH out - so you should be fine.
After a month it is usually ok to use clippers if your healing went well. You should always double check with your doctor.
Some doctors shave or cut their patients hair even a day after surgery. One month should be no issue. Use common sense, and be careful around the area.