Thompson center rifles are great and easy to clean (I have an Omega), but would not be my first choice if you ever plan on shooting conicals. T/C rifles are not built to for conicals. If you only plan on hunting in KS and only plan on using sabots, then by all means, T/C can't be beat.
Also as stated, some are not built for open sights (too straight of a stock) but work well with a scope ( my Knight KRB7), but it shoots sabots and conicals well.
Of course, my Knight LRH shoots sabots and conicals, and does well with open sights or a scope.
Welcome to the wonderful world of muzzleloaders, where there are as many choices as all other forms of hunting!