Yes it's very safe to order your checks online as long as you use a reputable and trusted check ordering website.
I order my checks for my checking account online and it's never been an issue.
I've gotten my checks safely and on time and it's much better than having to go to the bank to have checks reordered.
I find it cheaper to order my new checks online than to go into the bank to have them order the checks.
I use checks unlimited to order my checks and they really cheap and have fast shipping as well.
You can order your checks online or through the bank but for me it's much cheaper to order the checks online than having the bank order them for me.