I would not think it is much cheaper, probably the same, but the bottles are expensive (I think about 50 euros)
This sounds more complicated as one has to go to the filling place which is not practical for heavy users. I think that it is OK for me as I normally only need two bottles per season.
On the other hand there are marinas that take empty bottles to the filling place several times a week. So if one knows which one those are and at what time they do it, it could be very simple.
And most of all I really dislike the very rusty steel bottles.
But I was not sure whether the new ones are strong enough - nobody in this forum mentioned that, so I guess it is probably OK.