My first neoprene drysuit was an Atlan and my wife had a great deal of success with hers as well.(I now have an O'Neil 5/7mm neoprene drysuit and the cut of the suit is a little snugger but they are otherwise very similar suits with the exception of the thinner neoprene arms on the O'Neil.)
In my experience a modern neoprene dry suit does not require much if any more wieght than a trilam with the heavier underwear required to be comparably warm. Older neoprene suits had a bad reputation for needing a lot of weight due to air trapping from chest mounted exhaust valves and due to what tended to be very loose and generous tailoring.
I have also had mine down to 150' in 35 ish degree water and have noted no significant loss of insulation value with only light polypropolene fleece hunter type underwear to wick away sweat and add some minimal insulation. Even at depth I have always been warmer in severely cold water than in a trilam with 400gram thinsulate underwear and dry gloves.
The pros for neoprene seals are that they are extremely durable and very hard to tear, and if you manage to tear them, you can easily repair them. They are also much warmer as they do a much better job of insulating your neck where large blood vessels run close to the surface.
The con with neoprene seals is that they are not ammenable to dry gloves, but in my experience, the neoprene suit is so much warmer that you do not need dry gloves as with your core temp being higher, your hands will be and feel warmner in wet gloves than in dry gloves in the generally cooler trilam drysuit where your core temp takes a greater hit in severely cold water.
If you get a leak with a neorpene suit it tends to be self sealing due to the stretchy nature of the fabric and you end up diving a very efficient semi-dry. The same size leak in a trilam usually means a very wet arm, leg or torso and a very cold and miserable dive. The same thing can be said for wet versus dry gloves - a small hole in a dry glove means a totally soaked and cold hand while you hardly notice in the wet glove.