You can actually get maf, boost and many more similar data out of ecu with elm327. Even from hdi motor, though this seems to be on the case will it work. So not so crap but only a tool of reading real time data or resetting SOME faults.
ELM cannot read any kind of memory- So no chiptuning.
technically for some ecu's it could (and can). But it's not feasible and some of the limitations of the elm firmware (i.e limited length of messages) would prevent you writing back.