Hogsy.
Let me see if my analogy traverses the pond succesfully. The ProQ (I will refer to the Napoleon as a ProQ) is like a Suzuki Swift. The WSM is like a Lexus ES350.
The swift is affordable, and will certainly move you from point A to B. Like most modern things, it is fairly reliable, and will last with proper use. It is NOT anywhere near top quality, and will never find itself on a list of most reliable cars. The Lexus is a premium car, with a much higher price. It will however last as long as you want it to, and perform very well it's whole life, unless you want to sell it, wherein it will retain a good bit of value. It is always among the most reliable cars in the world, even though it touches the "luxury" category. It performs very well.
Specifically:
- ProQs are made of a thinner material, which also has a thinner, more matte like coating on it. Unfortunately, I can not give you specs, but plinking a ProQ with the back of your finger, and then doing the same to a WSM is like plinking a foil pan and then an alluminum pot. The WSM is STURDY. In addition, the true porcelain finish on a WSM is far more receptive to cleaning and durability than that ProQ matte.
- The proQ has a basket, not a grate with ring. You might think this sounds great, but in reality, the basket is a little small, and not quite as sturdy as the grate and ring on a weber. In addition, in ALL the ProQs I have used, I had to modify the basket and raise it about an inch to get proper air flow from the vents.
- The proQs legs are either dangerous, or sub par, depending on your point of reference. I HAVE seen someone using a ProQ where the legs bent (and the thing tipped) while using it. Bluntly, they are poor design, and a little weak.
- Someone mentioned they thought the system was 16.5 inches. I don't know about that. I will say the size of a complete proq seemed to be between an 18.5 and 22 WSM. (Bear in mind the company also sells or sold stacker conversions similar to the cajun bandit that were weber sized). Replacement parets .... I dunno. I do know where to get Weber parts. Easy.
- The stacker concept is an interesting one, with the option of adding another cooking section. In practice, it is just a little unwieldly, and it does increase variance in cooking temperature.
- Which brings me to cooking temperature. For the reasons stated above, and others that may be mysteries, the ProQ simply is not rock solid, especially out of the box, like a WSM is. It can be used. It is not an overwhelming amount of work, but when compared to the set it and forget it nature of a WSM, the two are not close.
One interesting thing about the ProQ is that I do believe thought and effort goes in to it's design. Specifically, there are things that seem like a good idea, but don't work for me in practice: For example, it has clips that hook the cooking sections together. This sounds really neat, but in practice, if the pieces are well made, this should be unnecessary. And taking two sections off at once (clipped together) is a little un wieldly anyway. The built in therm is nice, except it's accuracy is dubious, especially when considering that variance of temps throughout the unit. And besides, the WSMs have them now as well. The probe eyelets are nice. Of course I added them to all my WSMs when acqired ....
If you have any other questions, I would be glad to answer, but truly the best explanation is "they aren't made as well". There is no doubt, they will get you from A to B, but you will do it more comfortably in a WSM.