It's about as far down the ladder of steels as it's possible to get. It's not as strong as cro mo, so more of it is required, in the examples I've seen it's also a rolled plate rather than a manufactured tube, so it has no butting. The one example I've ridden had non of that springy steel feel that makes a good frame. though it's all subjective. When you think how cheap a double butted cro mo tube set would have cost the manufacturer, I think they would have spent the extra few quid if they wanted to build a decent frame.
Having said that, I'm sure people ride thousands of miles every year on such frames. If for some reason that's all you can get, it'll be loads better than nothing but if possible I'd look for a better frame.