I recently made the switch to Kev/Zx hybrid, coming from syn gut/poly (which I had been using for 2 plus years). I use a Babolat RDC to check dynamic tension coming off the stringer, then check it periodically. This way I figured out what DT reading was my "sweet spot". I felt I had the poor man's "Champion's Choice", with a string cost below $3/ and about 6 hours of playability.
I had actually been an early adopter of Kev/Zx when Ashaway first introduced it (I had experimented with Dynamite and Zx/poly hybrids as well). Having the string break when tying off the last knot may have been the deal breaker for me originally.
Earlier this year I was struggling with consistency on court and part of that was a feeling of hot spots on my racquet. I tried changing up the main (different syn guts, a multi, Dynamite). I liked the initial feel coming off the stringer but I was not happy with the consistency after 2 or 3 hours of play time.( I also tried Sergetti proportional tensions).
For the past 5 weeks I have been using Kev/Zx and it's been a game changer. I manually pre stretch both the Kevlar (minimal length gain) and the Zx (10% length gain). Stringing time is almost doubled as I let each pull on the crosses go for 60 secs before clamping off. There is a 5 or 6% drop in DT over night, then another 13 to 15% after hitting (which gets me in the same 47 to 49 range I considered my sweet spot on the syn gut/poly hybrid)
The solid, consistent feel this string bed yields is addicting. It's helped from all areas of the court, baseline, mid court approaches and volleys.
I am surprised by the range of DTs I find playable. I notice less power at 57 but it's not uncomfortable. Of my 4 racquets the oldest string job (4 weeks) is at 47 and playing just right. I have strung two of my racquets using the Sergetti pattern, I am interested to see if that yields any noticeable advantages (current DTs are mid 50s on both racquets)
For me there are two negatives with the Ashaway Kevlar/Zyex hybrid.The first is the cost of the string per string job ($9.40 per if you buy reels on sale). Anything over 18 hours of playability makes that a wash. I am currently at 20 hours on the 1st of my string jobs.
The second negative is the ugly tie offs of the crosses. Big, fat, ugly hand pulled knots
FWIW, the 4th racquet I just strung I had purchased used in June, the previous owner had used Champions Choice (Wilson Nat gut mains with Lux crosses). Normally I would cut out a string set up when buying a used racquet, but on this one I checked the DT, got a low 50s reading and put it in play.
It was nice, more consistent then my poor man's set up but I cut it out with out regret last week.