Understatement? I would have thought ουσιώδης might be nearer the mark or at least "απαραίτητο ! :-)
It is a bit tricky to translate βολικό as it has more than one meaning. It means convenient but also comfortable. Here, I see it as 'I find that the steering wheel works for me, it is well designed, I do not want to make any adjustments etc.' rather than convenient, which as you point out is an understatement! But can a steering wheel be 'comfortable'? To be fair, out of a car-related context where steering wheels rule, this could make more sense: "Oh I see you added a steering wheel to your coffee machine - how convenient!" :D
Thanks D-. To be fair to Duo I was having a bit of fun at their expense. But yes you are right, if you were small you might well find some steering wheels convenient and comfortable.