I own one, not the 'Uncle Mike's' marquee, but exactly the same thing, I picked it up at a show for 15 dollars.
It is made by liberty or something by that name.
It is very easy to convert, as advertised, the retention is okay, thumb break.
I am happy with it for what I paid, I probably would not pay over 25 for it at the store, but it does work very well for what I use it for.
For what you need it for I think you would be satisfied.