Well, I don't know about anybody elses experience, but I picked up a cello from an antique store about 7 or 8 years ago, it's no Amati but it's not a complete learner instrument either - it's the sort of low priced instrument that you might get as your second cello purchase if you were upgrading from a school hack. It was sitting in the window, stringless and unloved so I bought it on impulse.
I went and got myself a bow, a set of dominants, spent a little bit at the local violin repair store getting a new bridge and the soundpost refitted and then took it home to try out.
Since I've played unlined fretless for years, I found that I quickly adapted my left hand technique to the cello's scale length and since my fretless vibrato technique is already cello-like, that came completely naturally. I also took to the 5ths tuning without too much heartache, so I could play in tune, with the correct vibrato technique very quickly.
Bowing was a different issue. It took some practise to get the string to speak with sonority and to speak when I wanted it to, but after a bit of practice with how much rosin to use, how much bow tension to apply and how much pressure to exert I could make single string playing pretty mellow. Changing to different strings to play scales and arpeggios was more challenging, I would be doing OK, then as I moved to the next string going either up or down a scale I was often rewarded with a cat squeal of scraping harmonics rather than the mellifluous sound of a nicely bowed cello. I didn't have a teacher, just watched orchestral players on the TV and noted how they held their bow and the bow tension they had. Like anything else it just took a bit of practise but after what seemed a ridiculously short period of time compared to learning other instruments I was accompmanying my kids (both Grade 8 violinists) playing little string trio pieces (quartets without the viola basically) and playing along to Barber's adagio. I would NOT have been able to do this as quickly as I did without having had a secure understanding of harmonic intervals, fingering techniques and good intonation from playing fretless bass - I really didn't have to teach my left hand anything - Oh, except that technique when you stop the string with your thumb when playing high up on the fingerboard, but that came easily enough
I would never have made Carnegie Hall but I was good enough to play to family, friends and small informal concerts and sound OK. Never took it too seriously, never claimed or tried to be a serious cellist, just as a bit of fun, but at the same time it didn't do my bass practice any harm either and I seriously pondered tuning my 5 string fretless in 5ths for a while
The Cello is behind me in the corner right now, sadly without a bridge because it snapped when I was tuning it one day