Take this for what it is worth, because I actually don't even know what the Lionsteel SR2a is (well, just looked at a picture of one, seems hard to compare it to a PM2...), BUT... the Spyderco PM 2 is BY FAR my favorite knife (currently own three, despite the difficulty in obtaining them at a reasonable price) and this is particularly relevant because I AM NOT that much of a Spyderco fan in general, because I find their knives too expensive for me generally and I normally am not fond of the spyderhole because it makes their knives too wide in my pocket.
The PM2 fits in my pocket well though and I LOVE the compression lock (THOUGH I seriously have an issue with the fact both of the new ones I purchased required adjustment to get it working properly, which should not be required on a knife at this price level, and I personally think Spyderco's warranty dept s*cks... but when you figure out how to adjust it, you can get past this). Just overall the perfect size, weight, everything. I do prefer to add a Cuscadi geared backspacer though, which makes the grip feel a bit better for me (though getting the lanyard insert off to install it is bit of a b*tch...).