I’ve only typed on uniform 45g Topre keyboard for about a half hour twice (once a HHKB, and another time a Realforce), and on 55g and variable Topre boards for a few minutes... so my opinion shouldn’t be taken as authoritative.
Anyhow, I didn’t find typing to be painful, only slightly slow and not very inspiring. Felt like a very nice rubber dome (smooth, solid, etc.), but I despise rubber domes. I give Topre a 6/10 for overall experience after multiple quick impressions.
Topre have one huge advantage over regular rubber domes (either the membrane type or the conductive-dot-attached-to-the-dome kind) in that they actuate before the switch goes all the way to the bottom, and they actuate very reliably. Thus, the key to comfortably typing on Topre boards, as well as certain other switches, like stiffer Alps switches, is to practice using only the amount of force necessary to get past the tactile point of the switch, but not excessively much more: try for loose and springy, not hard follow through. It also helps if your wrists/palms aren’t resting on any surface, so you have the whole movement of your arm to absorb any excess shock. Many (most?) typists used to using rubber dome keyboards or scissor switches tend to mash the keys down with substantially more force than necessary, sometimes like 2–3x more. This results in hard impact shock at the switch bottom, which is really nasty for your joints when you do it millions of times. Unfortunately, on a regular rubber dome that actuates at the bottom of the stroke, you’re often forced to mash the keys because they won’t reliably actuate otherwise.
Cherry MX switches help reduce this impact by having a spring which gets progressively harder to push down all the way to the bottom, which means that even if you use excessive force to actuate the switch, the spring can usually absorb much of the shock. In return, Cherry MX switches (and other mostly linear switches) make your fingers do more work overall.
Clicky Alps switches (and similar switches like SMK, Omron, NEC, etc.), buckling spring switches, etc., reduce the impact by making the force drop after the tactile point very significant and sharp. This clear feedback helps your fingers to avoid putting too much force into the keypress.
With Topre (and some other switches like Burroughs switches which use a torsion spring, or brown Alps), the feedback is rounded, more subtle. As a result you need to spend more intentional effort calibrating the amount of force needed to type.
Personally I think it’s possible to design switches that get the best of both worlds here, but most folks designing switches historically haven’t thought all that hard about it. My favorite solution is the beam/plate spring type switches such as the Marquardt “butterfly” switch (though it’s slightly too stiff for my taste), Alps plate spring, or IBM beam spring switches. Buckling springs would be perfect if they actuated 1mm earlier in the stroke, had a slightly softer landing at the very bottom, and had a springier upstroke.
