"send us a check in the mail (5-10 days to get here), then finally ship it for them "
We are in very different businesses, obviously. What works in one industry may not work in another.
They are no delays involved by buyers (mostly well established seniors) sending me cheques (checks). Purchases are sent immediately. By the time I get the payment (three to five days later), they receive their purchases. Give or take a day or two either way.
That trust factor is an important factor to make customers come back.
Cash flow wise, it makes little difference, as cheques (checks) get deposited in my bank accounts immediately upon receipt. PayPal payments sit there until transferred, held for several days by the "system".
I would not suggest it if you sell computer games to the 18-25 crowd!