To me, I wouldn't spend the money to have Thermapen instant read technology on something I dont need instant read technology on. Keeping these in the meat, be it in the oven, a grill, or smoker, nothing is going to change drastically in the time it takes the temp to update. That and the meat temp doesn't change in the time it takes for a "regular" leave in meat therm. I have a cheap Polder, and a foodnetwork one, and they work fine.
Now all of that being said, if you have a thermapen and just want matching therms, go for it. I am sure it is top quality and will last forever. I may eventually get one but not on the immediate horizon. I am actually really interested in the Maverick competition to the thermapen at a lower price, and it has a backlight. You can't have too many meat probes.... and therms... and mortar and pestles ... and grills ... and knives ... and smokers ... and guns ... and women.