TLDR version: Gliss definitely has its quirks but in my opinion it's benefits can outweigh the downsides in certain applications. It’s cheap and casts amazingly, but only get the transparent (white) colour - all other colours are a problem.
For context, I mainly fish ultralight, targeting bream through to Salmon in the salt and bass in the fresh. I've been using 4Kg Gliss (transparent) as my primary line on my ultra-light setups for about 18 months now. I previously used 6lb 8 carrier braids (like J-Braid or Siglon). Originally, I tried Gliss out of a desire to save a few dollars - I had a few reels to spool up and the $60-ish dollars per reel was starting to hurt.
Pros:
It’s cheap! A 150m spool of 4Kg Gliss is around $20, compared to $35 for the same spool of J-Braid. Obviously j-Braid comes down in price significantly if you buy in bulk, which you cannot do with Gliss.
Gliss is incredibly thin for it’s strength rating. 4kg (~9lb) Gliss has a diameter of approx. .10mm (For comparison 8lb X8 J-Braid is .13mm). This is particularly useful when using Gliss on rods with extremely small micro guides - it lets you use stronger lines than you might otherwise be able to fit through the guides.
It is extremely smooth and has a very low friction coefficient. This results in what I believe to be Gliss' best quality - Castability! This thin diameter combined with incredibly round, smooth profile results in a significant improvement to casting distance! It is affected by wind less, and has less drag in the water. It feels so nice to cast – it’s hard to explain, but it just flows off the spool! This really cannot be understated & is the main reason you would use Gliss – its quite a unique sensation!
As a side-effect of it’s thin diameter, you can fit around 20% more on a spool. Not a major advantage for some people, but can help counter some of the downsides of Gliss.
In most other ways Gliss has virtually identical properties to regular braid – almost no line memory (In the transparent colour anyway), takes on very little water and floats the same as braid.
Cons:
Due to how thin and slick the line is, knots will slip more with Gliss, which limits your leader knot options. You will have to be proficient at FGs or modified Albrights (sometimes called an Alberto) - Double uni, blood, surgeon and most other knots all slip, and cannot be relied on. If you fish straight braid through to your lure or hook, I don’t think Gliss will be suitable.
It is definitely less abrasion resistant, even compared to braid. If you fish near tight cover, you might need to run a longer leader than you would normally. I usually tie on several meters (around 2 1/2 rod lengths) of wind-on leader.
People report a higher number of wind knots with Gliss. I had more wind knots when I first starting using Gliss, but it seems to have stopped. Not sure why.
The transparent/White colour can be hard to see, particularly in low-light or in the dark. This is particularly an issue because;
All Gliss colours other than transparent have a coating that causes the line to have memory, results in more wind knots and makes knots even more likely to slip. This is so bad that I cannot recommend any colour other than transparent.
Gliss can get kind of “fluffy” over time. This is really only happens in the last foot or so of the line, so it’s easy enough to deal with – I just snip off a bit extra when I retie my leader. This does mean you go through your mainline faster, but is countered by the additional capacity afforded by Gliss.
Should you try it? I really like it, but I don’t know if it’s better enough than normal braid to warrant a change. It’s a good bit cheaper and is really nice to fish with, but I wouldn’t unwind a full spool of braid to swap it with Gliss. For ultralight applications it can provide significant advantages over regular braid, but in the heavier weight classes, most of those advantages are less noticeable. For $20, it’s worth considering when you next respool, if only as an experiment.