All rads no matter where they are should have a valve , if not a trv then a manual valve , even rads in bathrooms have them , yes you can do with out but why ? towel rads also . also if you ever need to replace the rad due to failure or to remove for a power flush then the new rad will fit straight back in as they are "generaly" standard in sizes , ie 600 , 650 etc . Also a valve will make it possible to "balance " the system . If you dont you may find some rads get hot and others dont or just get luke warm .
I would not bother with ISO valves as it is just another valve , but if you do , make sure it is a full bore internal diameter as most are alot smaller in bore . and can affect the flow .
I hope this helps , kind regards Sam