It really depends on your current weight, unless you are currently obese, I would imagine it would be difficult to lose that weight healthily in a month.
The problem with taking it off so quickly is that it will go back on that quickly.. are you comfortable with that? Half a stone would be a more manageable goal. This is assuming that you're not obese.
There us no reason whatsoever to assume that because it comes off quickly it won't stay off it's not true. It's completely inaccurate to say it'll go back on
It's not how you get the weight off that influences your success but what you do once it's off
Well I have lost 2st 7pnd in the last 4 months but wanted another stone before my holiday. I think I'll try 10pounds as this is only 2.5pnd per week. More realistic