Used them for year on different boats, do what they say on the tin, plane a lower speed, encourage bow to drop etc.
Ive never had an issue with steering,or felt any il effects. My current boat has has them fitted and has done for 15 years, seems to still be functioning fine
Years ago had a 4m dory, heavy old thing wouldnt plane with the 15hp we had lying around at all, until we put on the dolefins then it worked OK, slow but it planed.
They are like bovril, either you love them or hate them, and you wont convince either camp to change their mind.