I got an original JetBoil PCS at an REI scratch and dent sale. I've used it for several years and here's my take.
Mine came with the pot adapter. It allows me to set any old 1 or 2 liter pot on top of the stove, if I should want. It works fine for this. Further, this burner only puts out say 1/3 or 1/2 the BTU's / hour that other common butane stoves put out. My SnowPeak puts out something on the order of 10KBTU's/hr, while JetBoil only does 3K or 5K, can't remember. It's burner is optimized to feed heat into the finned heat exchanger on the bottom of the proprietary pot. 10KBTU/hr would overwhelm it's ability to accept heat, hence the smaller burner.
That said, when you use the JB burner w/ adapter on a conventional, plain bottomed pot, it won't heat/cook as fast as a conventional burner. Maybe that's not a problem? It hasn't been for me.
I have cooked plain white rice in my JB 1L heat exchanger cup, just to see if it could be done. Whilst something of a fiddly stunt, it absolutely DID work. Enquiring minds needed to know. Later models may or may not have a nice enough simmer to facilitate cooking rice.
The biggest technical issue with JB is the JetBoil Sol Titanium. The issue here is that in the never ending quest for lightness, the cup was made of a material (titanium) which can't absorb heat fast enough from the fins. In consequence, the fins can get hot enough to melt into a tangled blob! So, just avoid that particular model. All the rest are fine, if they have the form factor and functionality that you feel you need. This issue is well documented in the backpacking press, complete with online pics. Their other models are great.