The big advantage is payload and total number of various options you can have on a 600. You can get a 600 @3.5t but payload will obviously be more limited. All UK 680s are 3.88t so it's moot if that's the van you are considering. A lower vehicle tax is also a benefit, currently £171 per year. I've not found any particular disadvantages in the UK (I have a 3.88t 600) as the vast majority of our roads do not have tolls but on mainland Europe tolls in some counties are higher and/or more of a faff (eg not available online/digitally). Speed limits are different and vary by country, including in the UK. Also anecdotally I've noticed >3.5t restrictions seems more common in the EU, no idea why, could have been just the areas we have been to. As you know you do need a C1 to drive anything other than an EV >3.5t (EVs allowed up to 4.25t). If you took your test pre-1997 then you have that be default. After age 70 you will need a regular medical to keep that category on your license. In the EU there was a directive passed earlier this year to allow the standard B category license to be used up to 4.25t on motorhomes and some other vehicle types and it is now just a matter of time before its rolled into law by each of the member states with some possible variation in how they implement. Last year there was a UK consultation on upping the B license to a higher number, perhaps back to 7.5t per the pre-1997 license but at a guess if it ever does change in the UK we will likely follow the EU and restrict to 4.25t especially given the situation with EVs being already allowed at that higher weight.
