Grass fed AND grass finished is outstanding and uncommon. Still plenty fatty with big impact on flavor and tenderness.
My son-in-law's family raises beef cattle, angus, and they are grazed (grass-fed) then finished on forage with a supplement concentrate of alfalfa, soy husk, and other high-quality forage for weight gain. Produces some awesome tasting beef with the right marbling and fattiness imo, but leaner somewhat than grain finished or grain fed entirely. They also do some in higher confinement (although not total confinement) to increase fat stores, as foraging reduces fat stores, and they do some grain finished for some customers. We typically get a half beef from them every year and a half or so, which ends up being a rib, long loin, and sirloin primals, that I then dry-age for steaks. We also get maybe 200 lbs of ground beef, and a couple hundred-ish pounds of other random cuts/roasts, including 2 tri-tips and 2 picanha. It has been a revelation. I usually get around 25 nice dry-aged steaks, mixed between new york strip, loin/sirloin, ribeye, etc. We also get a few really lean roasts, like the sirloin tip roast, which is just a hunk of muscle with almost no intramuscular fat, and we slow roast that at 175 degrees on the smoker for 4-6 hours until it hits 135 internal, then we thin slice it for sandwiches, which gives us 6-8 pounds of premium slow-roasted sandwich meat. The brisket we get is usually a little smaller than I like to smoke so I cook it Italian beef style with a nice jus and make italian beef sandwiches a few times, as it still generates a good 20 lbs of finished meat. We have loved having this kind of access to premium beef. Most of the cuts we get as family are somewhere between choice and prime, sometimes full-on prime, just depends on what they are doing to butcher. They usually use butchering for family to cull the herd or for specific animals that might not do as well at market, or they just take a nice one that is fully ready and we get a real treat with prime beef for a year and a half.
There is no doubt the grass-fed beef has a different flavor. Some like it, some do not. We have had a few funky ones for sure, when the forage has had more sage or other weeds of different kinds in the pastures, or if it was a little bit of an older cow. Mostly though we really like the grass-fed flavor. Grain-fed tends to be more neutral in flavor and it is what people are used to, although my SIL has eaten grass-fed his entire life so when we cooked a few tri-tip from a local butcher he commented a lot about how it tasted bland and kind of boring and asked why that was.