MC4 is a proprietary connector made by the company Multi-Contact (now Staubli). T4/H4 and others use the same form factor. Because the MC4 is proprietary, there is no industry spec that all the variants are built to which guarantees compatibility and interoperability. They're all based off the original MC4. But Multi-Contact does what they can to keep the market to themselves, including dire warnings that the earth will be riven asunder and death and destruction will result if they're interconnected with competitors products.
I wouldn't worry about T4/H4/MC4 FUD at all for an RV scale system. For a large fixed system putting hundreds of volts and tens of amps through them, sure - stick to one brand. But if you're putting a few panels on an RV, and they come with "MC4" type connectors already installed, I wouldn't worry about finding connectors from the same manufacturer to complete the system. They're all made to be interoperable, despite the dire warnings.
Not sure why Almot thinks Amphenol is German - their original name was American Phenol, and they're US (they do manufacture worldwide). Staubli is Swiss. T4s are made by Tlian, a Chinese subsidiary of Canada Solar.
