I have always used leaders of different types & tapers for different things so I change leaders often. As long as I can remember, the leaders I bought had loops on the end so doing a loop-to-loop connection seemed the simplest and most logical way to quickly swap out a leader.
100 years ago, I nail knotted a short section of heavy mono to the end of my fly line, coated it with Pliobond and tied a small perfection loop to the end which was my MO for leader attachment until I stared buying Rio lines with a welded loop...
I use more Sci Angler's lines than Rio lines these days, however I have never looked back on the loop-to-loop connection. Even the REAL silk lines I use on my bamboo rods have a woven loop at the end.
There is a trick to the smoothest connection...
You HAVE to make sure your connection looks like a 'handshake," like THIS:
NOT like a "cow hitch," like this:
It's also important to take a look at the connection once or twice while fishing because pulling the connection in and out of the guides can cause the loop in the leader to slip down from a hand shake into a cow hitch.
In regards to issues, I've had two loop failures in my life, but NONE resulted in the leader separating from the fly line and no failures with a welded loop.
One was a failure on a braided "leader loop" that you attach to end of a fly line WITHOUT a welded loop and the second was on a loop woven into the end of a real silk line.
On both of these failures the handshake loop-to-loop was so secure, the connection held despite there was only one loop so I just continued fishing.
SINCE these issues, I now work a little UV-Knot Sense into the area where the loop junction is formed and cure it with a UV light. I also do the same thing with Shorb Loops on furled leaders and the woven loops on the ends of braided butt leaders.
I have never had a problem since...
In regards to UV-Knot Sense, I've been carrying around a tube and one of their little UV lights in every fishing bag, box or kit I use because it is so useful. You may only need once in a blue moon, but when you have it
with you, it can save the day!
I've used it on nicked fly lines. failed leader or line loops, knots that hang-up or connections that need some abrasion resistance; even waders in a pinch.
I'll also add that the NEW pocket sized "Nano" version of their UV light is 1000 times better than the old mini light that was prone to getting turned on by accident and used PIA small LR44 batteries.