Great Conversations !
I own all (4) of the SparkFun RTK products mentioned Plus the other (2) which are the RTK Surveyor and RTK Express. Of the (4) mentioned in this Thread- each one of them are better at certain particular applications.
The Surveyor and Express were how I began my journey into the U-blox F9P chipset.
The F9P was what convinced me that inexpensive hardware could complete with the performance of my expensive Professional Equipment.
The obvious progression was the Facet with a cleaner form factor, and later the Facet L-Band.
Then comes the Torch, which isn’t related at all to the previous SparkFun hardware. It uses the UM980 chip, a much smaller helical antenna, and adds the L5 frequency.
And now the most recent, the PostCard with the new LG290P chip.
But it’s actually impossible to rank the (4) devices in any order.
The $700 Facet is a proven winner. Coupled with an appropriate correction source (just like any RTK), it’s a beast.
The Facet L-Band is like an Easy Button for GIS work, we don’t need to teach GIS technicians anything about RTK, corrections, etc.
The Torch has a very slick form factor and adds L5 that is beneficial around tree canopy…
And the recent PostCard is impressive, considering the price-point.
It’s brand new, and the LG290P FW from Quectel needs a little bit of time to mature.
To muddy the waters even more, several new Products are now in the Source Code 
I own a lot of SparkFun GNSS devices and I don’t regret purchasing any of them. They are tools for the toolbox. There isn’t a perfect device for every application, but I can use any of the 4 models.
Just remember, you cant outperform your antenna or your correction source.
If I’m going to a Job Site where a bunch of folks will be, I’m generally taking the Torch.
If I need to PPP a new Control Point in a new area, a helical antenna (Torch) isn’t my first choice.
But if the Government banned all RTK GNSS and came to repossess mine, I’d hide a handful of PostCards in my pocket and be an Outlaw like Jesse James 