The two Deck Bags that I bought are the North Water Expedition ($68) and Peaked ($40) deck bags. The bulk of this review will be centered on the Expedition bag since I have yet to test out the Peaked bag.
The reason I chose the Expedition bag was because it was large and I have a lot of items that I like to carry with me. It also comes with some features that I think will make the bag more user friendly. At 14 inches long by 13 ½ wide by 4 ½ tall this bag is big. Big can work for you or against you (more on "against you" later). I paddle through the winter and with the lake temp around 36 degrees this morning and the air temp in the teens I have had the unfortunate experience of not being able to get to any of my gear because the hatch covers were frozen on. If you need something and you cannot get it, then it is of little use, thus the deck bag! The deck bag allows me to access those items that I need for winter paddling.
I used to keep items under my bungees, but those items literally froze to the deck and became worthless. Therefore, I started keeping things under my spray skirt, which would also freeze to the kayak quite often. My spray skirt fits very well, I have yet to pop it off accidentally, but it can be a bit of a challenge to get it back on even when it is warm out much less when the skirt is half frozen, so a deck bag seemed like the perfect solution. Now I have ready access to those items that I might need with out the fight of popping the spray skirt on and off.
The North Water Expedition bag is easy to install on a kayak with its built in Velcro system which is secured under your front deck netting. There are also 3 straps on each side of this deck bag for attaching additional items or making it into part of a modular deck bag system. I use these straps to further anchor the deck bag to the deck of my kayak because it tended to shift around a bit when practicing rolling. This is in no fault of the bag itself, its just that every kayaks front deck bungee netting is different.
I also use the straps for holding my Greenland paddle while emptying the kayak of water while practicing Paddle Float Re-entries. The zipper I really like because it has two small cords on it that allow me to open it even with neoprene gloves on and the zipper runs the full length of the bag so it allow you to open the bag completely up. In contrast, the Peaked bags zipper opens straight across and only allows you to store items that are small enough to fit though the front opening. Three other features of this bag I like are the zippered closed netting on the front of the bag, which makes it handy for accessing items without opening the bag up. The webbing on top of the bag for installing a map and two small plastic D-rings.
To help maintain its shape add a little bit of protection to items inside the bag is the polyethylene plastic insert. Just one bit of advice about the insert though. The company that I bought my bag from placed it in a box what was smaller than the product itself, which means they had to fold it up. This bends the plastic insert into an un-natural position what may or may not come out. What I had to do was place a heavy object on one side of the bag over night to bend it in the opposite direction. Now it's back to its intended shape.
So far, I have talked about the advantages of a deck bag, but for every advantage, there are disadvantages as well. Adding anything to the top of the kayak will alter its center of gravity and depending on your kayak, this may or may not be an issue. With my kayak, I only noticed a slightly greater tendency to roll from side to side with the deck bag on, but nothing what was unreasonable.
The biggest change I noticed was in my ability (or inability) to roll my kayak, with a deck bag on, you will definitely need more effort to roll yourself back up, so after you strap it on I think it would be best to try it out so you can see if it affects you ability to roll. Once again, this is not a defect in the North Water Expedition deck bag in itself; all deck bags to a certain degree will have this effect on stability to a certain extent.
One last thing, the Expedition is not a dry deck bag, that is an entirely different critter, so even if you can roll quickly, your bag will still take on a little bit of water, so store items in it bearing this in mind.
Like most other aspects of kayaking equipment, once you start looking into all of the various deck bag designs and options out their you will be amazed as to what's available. For a first bag I think the North Water Expedition is a good choice, especially if you need a lot of room. I would give the Expedition deck bag a 9 out of 10 rating. I'm taking one point away because it only comes in one color that absorbs sunlight instead of reflecting it and does little for making you more visible on the water so other boaters can see you.