Are the Truvativ powerspline BBs reliable?
The TruVative power spline BB is a decent, if inexpensive design, and is unlikely to have failed through a design fault. 

All bikes, regardless of price or quality level, require periodic maintenance.

One of the most common issues on a relatively new bike is the crank arms "seating" on the BB spindle, and needing the fixing bolts to be re-torqued.  This will happen on every BB and crank design, with varying time frames between occurrences. 

The Octalink BBs are known for loosing fixing bolts, actually. :) 

This is not "bad luck". But neither is it a design flaw. It is missed maintenance.  They should be checked every few weeks until you get a feel for how often you need to do the maintenance. FYI, every bolt on your bike can have similar issues, and should be re-torqued periodically. 

Unfortunately, as you discovered, a crank arm ridden while loose will damage the crank, and often the BB spindle, and it can be an expensive repair.