I fitted new Tiagra 9spd to my tourer this summer for an 8 week tour.
The shifters worked as advertised with no faults.
There are some issues when using low gears. They will operate any rear mech, eg Deore but 9 speed is quite fussy about adjustment and I could never get this right.
They will only operate road front mechs, not MTB ones so you are stuck with using a Tiagra triple shfter on an MTB chainset. It works but requires careful trimming. Unfortunately the trim function is poorly thought out and you can easily overshift esp from middle to small ring. You then need to shift back up and retrim, by which time you have lost momentum and actually need the small ring so you have to shift back down again.
I left the cable outers un-trimmed to route around the bar bag. It is an ugly solution, you can use v-brake style noodles but that limits the thumb position.
All in all, Shimano Tiagra is unsatisfactory for touring due to poor design. My previous shifter, Campy Mirage 8spd had better cable routing, better trim function, more robust innards and a built-in brake cable remove position. Unfortunately I cant use it with any current rear mech.