I've had many, many shoes Topy'd over the years, although none of my best-quality dress shoes. I don't bother with Topys on my EGs or Lobbs because I wear them relatively infrequently and am not worried about wear (although I am somewhat worried about slipping and falling on my keester). Pretty well all my Allen-Edmonds, Ferragamos, Ballys, and a few C&Js have had Topy rubber sole covers. This goes back more than 25 years and has involved perhaps 25 pairs of shoes. Not ever
has any sole damage occurred because of a lack of breathability; it's just a non-issue, and, in my opinion, is based more on (incorrect) theory than on any empirical evidence--at least if my own "experiment" (experience) is generalizable, as I believe it is.
I've found that the Topy addition does next to nothing to degrade the appearance of the shoes, being as thin as it is, and, in fact, is all but invisible except, perhaps, when one raises his shoes to cross his legs or something like that. Further, the Topy does seem to render the sole virtually indestructible, and makes the shoe stable and safe underfoot.
Interestingly, this issue about the detrimental effects of covering a leather sole with a rubber overlay comes up about every 6 months or so on the forums. Every time, someone points out the (in my opinion flawed) theoretical argument against this practice (a lack of breathability leading to damage to the leather sole), but, if I remember correctly, no one has actually witnessed any sole damage resulting from it.