Blimey, there's a blast from the past. Being an outdoorsy gurl both by leisure and profession I used to see (and use) these quite a lot, thankfully you hardly see them any more, they were such a footer, and have probbly gone the way of the lorrymans wrench (or hitch depending what part of the country you hail from).
They may be a footer but they are easy to do to the point where you can do them by feel so as easy to tie in the dark as in the day, and you're right they can be done from both sides, and if you can get the tension right can be undone quickly by running your hand up between the two sheets. You used to get them on covers for lorries and trailers where the loops were slightly elasticated and secured at the bottom by hooking the bottom lace/loop over an anchor point of some sort, the elastic allowed you to pull the whole thing tighter making it less prone to trouble from the wind; but of course the elastic didn't last for ever.
If I was fitting one I wouldn't be using a knot at the bottom, I would have the last lace elastic so I could easily pull it over on and off a hook but my experience is that the wind will always find a way to get in about this kind of tie method so it needs to be really well made with a good over flap, the correct length laces, and the last lace really tightly secured or you just give the wind something to play with which will eventually cause damage. I wouldn't say this method is any more robust than a really good zip but possibly for different reasons; I'm not trying to sound like a rain cloud but unlike with a zip every one of those laces has the potential to provide the wind with a little pocket to get in and buffet around, so can work well if made well but can can also get trashed pretty quickly in bad weather if not.
I think they look really nice cos I like things like that but on a more practical note the rope laces may have the potential to out live a zip but the stitching of the seams would need to be extra secure, a sturdy over flap thingy (I'm not sure what you actually call them) that maybe also had heavy duty snap fasteners or velcro and either a good anchor point for the bottom lace/loop or don't make it a loop so that you can tie it in a better more secure way, would be my suggestions.
Sorry that's a bit rambly