Man this is like throwing a steak. Just nothing but BEEF. Mine is in K3 and the plastic was top notch as always. Definitely more stable than a Zone. The flight plate was super flat nearing puddle top to be honest. If you are needing an overstable approach disc and really like Kasta, the Jarn is definitely a solid pickup. 

I bought a K3 Järn last month in hopes of it beating in faster than my K1 Järn to explore what a beat-in Järn is capable of. The Järn is what I've always wanted the Zone to be, consistently overstable in multiple plastics, a touch faster but not like a a true midrange (like a Justice). The shape of the rim is also great for skip approach shots. It's amazing BH and FH. I've tried the Zone, Mint, Harp, Slammer, Toro, AviarX3, and for my noodle arm, limited (basically only approach) forehand, and baby hands the Järn is money!

The K3 Jarn starts out much more over stable than the K1 Jarn. Very reliable disc fore forehand and the feel is amazing. I've had mine in the bag for about 4 months and it has not lost much stability at all.