My singles have 170mm cranks, our tandem 175. My stoker has much shorter legs than I. The tandem came with 170mm stoker cranks, but that long a crank made her legs cramp. The crank length on my singles is correct by the 5.5 * inseam in inches method. That same formula for my wife said she should have 150mm cranks, so I put those on for her last year. That totally screwed our seated climbing ability. She doesn't have the leg strength to get the power out of those shorter cranks at cadences which are powerful for me. OTOH her legs don't cramp and she's happier, so that's that. As I've said before, crank length is largely a gearing issue. Absolutely you'll need time to adapt your neuromuscular system to the longer cranks.
I assume "easier" means lower HR at the same power (speed). Yes, lower climbing cadence always reduces HR, but whether that's a good thing or not is another story. It's the same old story: lower cadence = increased leg stress and reduced aerobic stress. Perfect cadence and thus crank length, as the two are connected, is when breathing and leg stress are maxed at the same time. That's not a simple thing as both are modified by training.
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