For a commercial-grade termination, guaranteed >30dB @ 4GHz is almost as good as it gets. I have a bag of Huber&Suhner SMA terminations which I think are >32dB but they are significantly more expensive. For someone looking for a cheap "good enough" working standard, the MC seems easy to recommend. And if you buy 3, chances of getting one close to 40dB to ~3 GHz should be pretty good.
If you need guaranteed, tracable specs, then there's no way around getting a proper, characterized cal kit (and paying $$$ for that). But having some working standards, selected from inexpensive off-the-shelf parts, is a thing even in professional labs. Especially for design work or a quick pre-check, a dB or two usually doesn't matter and you generally want to avoid unnecessary mating cycles on the expensive stuff. Sometimes you can get away without calibration (and maybe automatic port extension) but sometimes you can't.