What's the catch with FRAM?

FRAM is great, however, the technology has destructive reads. Flash technology has a limited write/erase cycles, but the reading cycles are almost unlimited.

In FRAM, each read cycle actually affects the memory and it starts to degrade. TI states that they've found the FRAM has "Wear-out free endurance to 5.4 × 10^13 cycles and data retention equivalent of 10 years at 85°C". After some calculations this turns out to be around 2 years of constant read cycles or so (without taking into account ECC).

The reality is that for most low power applications, where duty cycles are low, this is not an issue. You will need to evaluate it for your specific application.

The limit in speed is also present, so waitstates will be added if needed. However, one solution is to load code to RAM, run it from there (avoiding the cycles on the FRAM) and avoiding the speed limit.

There was an E2E post on the topic here that discussed some of the ramifications.

A good App Note from TI about what the advantages of FRAM are as far as security is Here

From what I can see, the (main) difference between it and SRAM is it's slower, and the difference between it and EEPROM is it's more expensive.
I'd say it's sort of "in between" both.

Being a pretty new technology, I'd expect the price to drop a fair bit over the next year or so providing it becomes popular enough. Even though it's not as fast as SRAM, the speed is not bad at all, and should suit many applications fine - I can see a 60ns access time option on Farnell (compared with a low of 3.4ns with SRAM)

This reminds me - I ordered some Ramtron F-RAM samples quite a while back, still not got round to trying them yet...

The only real issue with FRAM is that for the really dense parts, the part of the market that drives volume and margin, they cannot yet compete on density (which is either a yield thing or a size thing - it doesn't really matter which). For the smaller parts (i.e. competing against older version of same technology) they do well.

So yes, it's a good fit for experimentation as long as you stay in the same size parts.