I've refilled them for years with a $5 adapter I got on Amazon many years ago. I see no risk. I can smell propane.
My method is this:
1. Put empties in the freezer for about 15 minutes.
2. Carefully set 20# tank upside down on the edge of a table outdoors or in well ventilated area. Has to be at the edge of a table to give you room to work around the nozzle. If this bothers you get a helper to steady tank but I've never had a problem, full 20# is stable enough on it's head.
3. Fill em up, one at a time, walking them directly from freezer to outside fill station. Screw small cylinder on to adapter/big tank with big tank valve closed, open to fill only when tightly attached.
4. Listen for gas to flow. It will be very audible at first and then trickle to a halt. They will not overfill. Keep a big crescent wrench handy because as you fill multiple canisters the adapter will occasionally get loose and you'll know it by gas escaping.
5. Pay attention to your small cylinders. They get rust around the top with age and this is where you have problems.
6. One thing I did at first was get a kitchen scale and weigh empties and then weigh them full. None are the same. There is a wide variance in the quality (amount of metal) in 1# cylinders.
I bear no responsibility for anyone blowing themselves up with this method. It's easy and just as safe as anything else you do with live fuel, such as cook.....or drive.....or maintain temperature in your camper or wherever else you use propane. In other words, I'm not really sure what the big deal is.