25% sounds a touch high to me, certainly for normal engineering role in tech (though I could well imagine it being more for niche or very senior roles)

12.5-20% was the typical range when I last dealt with them in the mid-late 2010s (usually varying with the seniority of the role). Perhaps things have changed to reflect the additional value they provide in bypassing the torrent of spam that's currently plaguing the recruitment process - but 25% still feels higher than I'd expect.

I agree that you can use this as an argument when negotiating a signing bonus if you're a direct candidate. Won't always work because the hiring manager usually isn't the person who's deciding whether or not to use a recruiter/headhunter (and their fee probably comes from a separate budget), but it's worth a try. I did exactly that when last changing jobs, and managed to get an additional 10%.