I used one for 4 years playing all the time, one Millennium Div1 event a month, one national like cpps per month and as much training as I could get in in between.
If you dont at least clean it, yes it will rapidly fail on you. However, this is the same for every gun. Any gun, poorly maintained, will probably fail.
The mini, etek, axe, pmr are all quality markers. These days, all you have to do is clean the gun and get it running nice, and it will keep up with any £1000 gun.
As for swapping out the mini bolt, personally I wouldnt. The efficiency gain, is like 30 shots. Its not really worth all the setting up and fiddling about.
The battery does seem low at the end of the day, this is true, but Ive never not put a fresh battery in a gun before a tournament before, so never bothered me. If you wanted, you can buy the new Shockwave board from KEE (its about $26US), which has a few improvements, like a proper Millennium setting, much much better battery consumption, and also if you take the battery out, you dont lose the settings. On the old board, if you remove the battery for longer than 30 seconds, the board resets back to default factory settings. The new board sorts it all out.