There are high quality converters out there, so some of the points raised here on safety and quality don't have to be an issue. See this for example, from Jerba who are a VW Registered Bodybuilder...
https://www.jerbacampervans.co.uk/vw-registered/safety-quality/
We looked at the Cali but chose to go with a brand new Jerba conversion because several aspects suited our intended use better. We prefer to stay off-grid as much as possible so chose the 4-seat layout with a rear kitchen and onboard cassette toilet - we can comfortably do 3 nights "wild" before we need services for our water and loo, and with a solar panel we virtually never take a hook-up pitch.
We chose a Wallas diesel-powered combined hob/heater, so we have no gas cylinder onboard, and no potential issues with ferries/tunnels or different cylinders in different countries - as long as we have diesel in the vehicle's tank we can cook and keep warm.
We still have 4 beds including a 150kg rated roof bed for 2 adults, and a choice of 2 singles or a double downstairs.
Jerba produce their own elevating roof. The roof canvas is cotton Ventile so it doesn't suffer from condensation, and all the vents are fully proof against Scottish midgies.
There are a lot of other nice little touches. Jerba aren't big on bling (although you can spec it to a fair extent if you really want) but they do produce very practical campervans.
Because the conversion was done on a new T6 window-van it counts as a "2-stage build" and so it's registered from new with DVLA as a "VW Jerba Sanna", body type Motor Caravan, but since the emissions are unknown because the conversion has altered the VW factory figures, it gets a taxation class of Private Light Goods and therefore pays £265 VED per year.
The 3-year VW Warranty is completely unaffected by the conversion (I took the 5 year / 80k miles extended warranty), and there's a 2-year warranty on the Jerba conversion work.
I'm not trying to knock the Cali here, just point out that there are alternatives and in the end it all depends on what you want from a van and what features matter most to you. By the time we specced all the options we wanted from both VW and Jerba our van certainly wasn't cheap, although I'm not sure exactly how it stacks up against a Cali. And I honestly couldn't say whether depreciation will hit us more than a Cali, but as we can see ourselves keeping it for 10 years all being well, that's not a pressing issue.