Looking to pick up a good all purpose AR and was looking at the M400 elite. Possibly for 3 gun later in life. The Tread is at a great price ($729 shipped) and looks good in reviews, etc. but I have no idea in real life how it is and, most importantly, can't seem to find the answer to a rather stupid question - am I limited to Tread accessories only or will I be able to add anything down the line I'd like? Thanks. Any thoughts and opinions are appreciated.