They are. I just bought some to replace my old flooded cell batts. Supposed to last 3 times longer plus can be cycled deeper. We'll see.
Looking at some units on Amazon, it appears the LiFePO4 batteries still run about 3.5X the cost of SLA (in small quantities). Is that consistent with what you’ve found? My SLAs (Walmart!) do sometimes last ten years. A royal hassle to keep filled, tho.