We have Shell ownership and have stayed at KCR II and Shell Holua Mauna Loa. KCR has more amenities, more open space, larger pool, restaurant etc. It costs more as well. What I read in reviews before staying at Holua, was that it was preferable to the Wyndham Mauna Loa. That might have changed as Wyndham now owns Shell.
We have stayed in one bedrooms three times at KCR, twice in the same unit facing BBQ and play area, and once facing the ocean. They do charge a daily fee for AC if you want it, and we did.
Holua is as described above pretty well. The advantage is that if you aren't in need of on site amenities it's a good money saver. Or at least point saver.
Both are on the south end of Kailua-Kona, which is nice, except that when you want to go to the best beaches it's about a 50-60 minute drive.
While we at Holua, about 5 years ago, they were upgrading units, though ours hadn't been yet. New TV's, furniture. So now everything is at least five years old. We had a couple of nights reserved there this June and then after a week stay in a 4 bedroom house at Mauna Lani Resort, followed by 8 nights at Paniolo Greens, another Shell property. All cancelled of course, so planning for 2021.