It would be nice if one could view the smokers in question in a store - open the hood, kick the tires, and the like. You can with some but not with others. And it can be a tad stressful.
As jted stated, the Auber is nice but not needed for most smokes. As a matter of fact, a remote like the Maverick or a
Thermapen for measuring internal temperatures of large hunks of meat is necessary; needed for the SI, built in on the CS. A great many folks are using the SI with no Auber and getting good results. The live with the temperature swings, learn their smoker's temperature management, and just settle back and enjoy the results.
I know that there have been folks who mounted the Auber probe permanently and for a while, it was unclear just where to place the probe. High up? Low down? Next to the existing probe? More stress. Fortunately help is only a post away. The SI is a lot of smoker for the money. My brother has the SI3 and he anguished over the temp like many do. No Auber, just a digital remote. He no longer uses the remote unless he wants to cook to an internal temp. All it did was add peace of mind.
Yes, if you want to permanently affix the probe, you have some drilling and wiring to do. And stainless steel is tuff stuff to drill through. While many have done this, I have no idea what it does to the warranty. It seems fool hardy to toss a 3 year warranty out the window. But many have integrated the Auber into their smoker with no ill effects. I suspect the Auber will fail long before the smoker does. The smokers are tough units.
On the CS, you pay more. True enough. But then all is built in. Smaller than the SI3 capacity wise, but judge for yourself how much capacity you need or anticipate needing. No programming, just set your temp, start and walk away. You pay for this convenience. The Auber is nearly as convenient.
Look at parts replacement costs for each smoker you are considering. Parts are free under warranty. But after the warranty? Be it a heating element, or a controller, consider it.
You are going to be one happy person with the food your smoker produces no matter which unit you get. Since you have the money, toss the price out the window and just consider the features and the size, and study the posts. Coulda shoulda woulda happens to all of us. There is no way to avoid it except to go with your gut.