I have been using En Plein Air Pro Watercolor Easel for half a year now. I still love it almost as much as I did on the day it arrived but I have a bit more perspective on its advantages, disadvantages and uses. So here we go:

Pros:

• Very lightweight (the easel proper, not counting tripod and shelf, is 1lb. 5oz)
• Extremely quick and easy to set up
• Fits onto any tripod via a standard tripod mount
• Thanks to that, you can manipulate the angle of the board any way you like

• You can buy the whole package with the easel, tripod, palette shelf, and carrying bag, or pick and choose among any of these. Since I already had a decent tripod (Slik Heavy-Duty Tripod with 3-Way Fluid-Effect Head and Built-In Bubble Level), I bought the easel attachment and the shelf.

• Fits into most backpacks, which means that your entire plein air setup can be carried in one backpack (the tripod can either go inside the backpack or be attached with straps outside).
• Both the easel and the shelf have holes for holding your brushes

• Despite being so thin and lightweight, the easel is actually relatively sturdy. It is made out of ABS plastic, which you can bend a little - but so far, it has stayed flat and straight.
• Has a lip on the bottom, so you can just prop up a sketchbook or sheet of paper against it without attaching it to the board
• Has a hook for hanging a water container - nice idea, but this is also going to the "cons" section below
• Compared to the heavy french easels with all of their paraphernalia, En Plein Air Pro just looks cool. Anytime I paint outside with some new people, somebody asks me about the easel.

Cons:

• The above mentioned hook for the water container is on the bottom right, which makes the easel board bend and lean that way whenever a normal size water bucket (like the popular collapsible water jar) is hanging from it. I usually just put the water container in the middle of my John Pike Watercolor Palette - 15 x 10.5 which sits on the shelf. It looks like the Original Series easel has the hook in the middle. I'm guessing, the hanging water container was interfering with the user's ability to reach into the back of the shelf/palette, so they moved the hook to the side. The new Advanced Series Plein Air Pro palette shelf lets you put the water under the shelf, so you don't have to worry about those hooks at all.
• Since this is a portable easel, you should probably expect to be limited in your choice of painting surface sizes. In the case of this easel, anything taller than 16-17 inches feels too big. It is definitely awkward to work on something like a vertical 16x20 piece.
• Because of the angle of the tripod legs, the shelf is tilted back, towards the center of the tripod, when all three legs are extended the same amount. To correct that, I make the rear leg longer, so that the whole tripod is leaning forward. This makes the shelf level but at the expense of shifting the tripod balance. I have had it topple over at the slightest touch of my 2-year-old. (Tip. Keep those toddlers away from your easels...especially if there is something on the easels that you care about). It looks like the Advanced Series palette shelf also fixes the tilting issue by introducing adjustable tabs.
• Umbrellas for plein air are not likely to work with this kind of setup. It would just be too heavy and throw the balance to the wind. But then, I don't even own an umbrella.

As with most portable setups, you have to watch out for that wind I just mentioned and weigh the tripod down. You also need to tighten the tripod mount screw quite well before attaching the easel to the tripod - otherwise, the board develops the tendency to slowly but surely rotate counterclockwise.

Because of the portability and flexibility, I use En Plein Air Pro more than my studio easel. I take it outside, I bring it to my classes, and I paint on it at home. If I didn't already have a large palette, I would likely get the Advanced palette shelf.