I don't think they come with trigger locks anymore. It's a safety issue. With a trigger lock, you might be tempted to try one handed triming and then you might be cutting a finger instead of a cord. I think they all have a double hand interlock now so you have to keep both hands on the tool.
I have the 40v Ryobi and it has been great. I've used it a couple of seasons already with no issues. It will cut up to 1/2 inch to 3/4 inch wood branches without stalling. I love the swiveling handle that allows you to easily rotate the handle in 45degree increments, which really saves stress on your wrists.
I also have the 40v brushless string trimmer and 3 of the 40v blowers, even though I only bought one. Found one in the recycle bin with a cracked tube (no battery) same as the one I bought with the adjustable handle and the other was a lower model (no adjustable handle) found at a garage sale for $30 or thereabouts.