I had Tiagra shifters on my 2015 Surly Straggler along with a Tiagra rear derailleur. The shifters & derailleur worked just fine, however I wanted under bar tape routing of shift cables (this is my first bike with brake/shifter levers "brifters"), and got a slammin' deal on a new set of ten speed 105 levers which included cables, housing, ferrules, tips.

The "touch" on the shifting on the 105's is lighter and I feel slightly less mechanical movement inside the lever, so I guess you'd say the shifting feels more "refined". It's subtle though, and I think that, unless you cycled a lot or were keyed into these things, you might not notice improvement. I guess I'm saying that shifting and braking feel different, but not necessarily better.

I decided to get a 105 rear derailleur (10 speed) to see if I get maximum benefit out of my shifter upgrade. I haven't installed it yet, but I suspect that, again, it will be a modest upgrade in performance. The ten speed components were a steal since eleven speed is the current big deal now.

My understanding is that recent & current Tiagra is solid, reliable and very competent.