The Lineholder's only real flaw is being a near Intro-Tech 'Mech in TRO3058, the most munchkin min-max TRO there ever was. It's a solid, dependable and reliable line Trooper, which, while not flashy, still gets the job done on a realitively cheap budget. It's the sort of thing that you'd see bulking out a Planetary Millitia unit or your average Merc command. It gets a lot of use in my games, and I rarely have anything bad to say about it.
...true, I do like the Linebreaker variant simply because it's so endearingly silly, but that's beside the point.