These radios date to the 1950s. Two different FM transmitters were used to sample the radios, but some cases the signal was sent directly into the radios’ circuitry. The tuners have RCA outputs which were used, but the table-top radios don’t. For those, the signal was taken from the speaker leads, after they were disconnected from the speakers.
The best way to think of these effects is as a set of tone sculpting tools. You get a lot of a tube tone, but the tube types used in the old radios aren’t the same you’d find in a nice tube preamp, so they sound different. Also, most of these programs also filter the frequency content in very noticeable ways, and all are different. This happens because of various other components in the circuitry of the radios such as transformers. Each program also has a unique harmonic fingerprint, giving this set a lot of variety. There are 25 different ‘flavors’ total, and 6 bonus stereo combinations (made by pairing up similar effects from the original 25).
This is a very cool set if you are into tone and especially if you are into finding ways to make things sound old. Used carefully and in the right context, you can also create something new.