I've written about both and tried both and I think the heat shrink method ultimately produces a better finished product. You probably saw my flat iron article or video -- I am not aware of anyone else writing about that as I got it straight from the guys at Scientific Anglers. However, I wouldn't go that route if you can find the right stuff. Heat shrink and a heat gun is the way to go.
What you want is clear polyolefin tubing. It's available cheap on Amazon. All you need to do after that is get a heat gun, which is like $15 at Home Depot.
The idea here is to liquefy the PVC coating while it is encased in the heat shrink, which will provide compression and also form a mold. The longer the length of line that you bond, the tougher the loop will be. But generally speaking even hack job loops are tougher than any knot you can tie to fly line -- I did test all of that using my boga and the welded loops were on average STRONGER than the rated break strength of the line (i.e. one loop survived being pulled to the full 20 lb. break strength of the line three times before it failed). No knot even came close -- the best knot was 90% of total line break strength (18 lbs. out of 20 lbs.) and several common knots were even lower -- sometimes much lower.
The thing about a boga test like that is it teaches you how few pounds of force we actually put even on the biggest fish. I've been using these knots to catch big stripers for years. I guess I just never approached putting 20lbs. of pull on them. After all, tarpon guides regularly set their drags at like 12 lbs. for 100+ lbs. fish.
Here's my original post with the knots and test results:
Topic: Knot Strength
The Double Surgeon's and Castwell Knots were tied with leader material only. The other knots were fly line to leader knots and you can see how weak most of them are. And I've been tying knots and rigging lines for years; all of these were tied correctly, I assure you.