Tekkai no Senshi is just another generic shounen manga that ticks all of those common shonen tropes: hotheaded MCs, tragic backstory, friendship-over-confrontation type of relationship, rallying cries, personal sacrifice, etc., but it does fall short in other way, the least of which includes the lack of a strong, dynamic, impressionable antagonist(s) and relatively short arcs. The only thing unique about Tekkai no Senshi is the premise that humans have grown extra biomechanical arms on their backs and that ripping off these arms would also end up killing its bearer. While there is a brief exposition of the Tekkai no Senshi world, there is not enough worldbuildingto develop a mature story that leaves its readers satisfied enough, partly attributed to the few number of volumes, and partly due to the very singular and myopic goal of defeating the final "boss".

Not much else can be said of this manga. If you want a short quick read of a shonen manga, you might enjoy this. Conversely, if you prefer a more mature and well-developed story with unique characters and a unique setting, you're better off reading something else.