Sorry, if I-beams are what you need for your application then sure, the K1s are the ones to use.
But they're made in the same factory as the speeding rods. It's just a big factory in China that makes forged rods for K1, Eagle, Scat, Yoshifab etc...
Your "few more quid for nice rods" are going to the same place in China, and your rods are coming from that same place. Anyone making "really nice" rods not in China will explicitly state where they're made, not beat around the bush with ambiguous terminology.
My experience with a side by side is with whiteblock rods, I had a set of 139.5mm whiteblock rods here from K1, and a set from Maxpeedingrods and they came in the same box (with different branding, of course, but even part number labels were the same format), packaged the same way, both made in PRC, same bolts, same machining, etc.
If you need an I beam, get the K1 because I don't see anyone else selling it. But for your application (less than 300hp) and presumably spinning less than 8500rpm, the cheap H beams would do fine. I've weighed them end to end and they've always been remarkably consistent within a set. I've run them over 100hp/cyl and over 8000rpm and the set in my audi had the 5/16" bolts. I wouldn't hesitate to run them. KLracing sells 158mm versions of them (in crank steered or piston steered) for not a ton of money.