I sat for the CFA L1 in 2008 (did not pass, but ended going up a different career route anyways), and I think the FRM is easier in some ways and harder than others. The CFA L1 exam has a huge focus on quantitative questions, whereas from what I can tell so far the FRM is more qualitative/conceptual (or at least the material from books 1 and 3 seem more conceptual).
Then there are areas where the CFA and FRM have zero overlap. For instance the CFA L1 covers a lot of financial statement analysis and IFRS rules/regulations whereas the FRM doesn't materially touch on it. And then the FRM has a huge focus on econometrics (my best guess is that the material at the very least approximates a masters level econometrics course) whereas linear regression is only briefly covered for the CFA L1.
A colleague of mine is currently in the middle of passing PRM.
While the concepts intersect with FRM, the certification approaches are quite different. Not taking into consideration 2 parts in FRM vs 4 parts in PRM, the latter requires way more calculations, AFAICR: matrices, differential and integral equations. If you're good at rather basic calculus, PRM is going to be easier to pass. It costs a bit more though, and apparently less popular than FRM.
Oh, and the PRM preparation materials are distributed in the protected *.pdf files, so that you're unable either to copy anything from them, or make readable screenshots... There IS a workaround for it, but it's rather off-topic in these forums, I guess.
And another colleague of mine is preparing for CFA L3. The overall CFA intersection with the FRM materials is within the 15% level, as he says. He passed both FRM parts with 1111, 21112 quartiles, if it matters (quite a whiz fellow, I'd say ).