I had the zflip 1, 3, and 4 and I just got the Razr+. I can't comment on longevity on the latter yet I can give a review on the zflip, specifically the 4.
Stay FAR FAR AWAY from it if you value your wallet. I had mine less than a year when I noticed some discoloration along the length of the center where it flips. Made a warranty repair request ticket with Samsung and was told flat out they would not honor any warranty on the screen, (turns out that discoloration was caused by microscopic cracks in the ultra thin glass).
They offered to give me a discount cost of $275.00 to replace the screen?!?!?!?!!! On a phone still under warranty that I just paid $1,000 for. I was livid but grudgingly agreed and they sent me a box with shipping label to send it in.
As luck would have it, UPS lost it and after a months wait I was refunded by the loss claim full value which I used to buy the Razr+.