When I measured my 4.25" stroker kit, The weights were very close to what I measured with a bobweight difference of less than 1 gram. I also checked the rod big ends with a bore gauge for roundness and taper when torqued with ARP Ultra lube, and they checked out fine. These were the older "I" beam rods, with the ARP2000 bolts, so I don't know if the "H" beam rods may be different?
I would not say the kits are perfect, and the bearing clearances are a bit tight for a race engine (around 0.002"), but are fine for a street engine.

I have my 4.15 stroker apart and the machine shop had this "balanced", but I am going to have it re-checked because the engine was not real smooth, and I will deepen the valve pockets on the pistons. I am curious if the machine shop may have made the balance worse?