Using an MVNO that is a separate entity from the underlying network (ideally with multi-network access) is a reasonable way to disintermediate your data from the carrier and throw a wrench in the works for SIM swappers who might crack one of the big three carriers postpaid provisioning and activation systems.
US Mobile, Ting and others are invested in maintaining separate billing infrastructure from their activation and provisioning infrastructure. I would avoid low quality carriers like Project Fi, MetroPCS and Mint Mobile where they are big carrier owned or have gone entirely to one network, but offer very deprioritized data access (eg: Tower delivers 400Mbps, but Fi users get 27Mbps despite the same carrier aggregation band combo in use) and no domestic roaming.