hmmm.... (im no pro but hay i will have ago)
Yes on a scale Plain bearing may be less reliability than ball bearing (thou i do not agree 100% of this statment)... but why would anyone make a turbo if it wasnt reliability, greddy/trust wouldnt be making plain bearing turbo if they were to go bang after 1 to 2 years....
There is nothing wrong with plain bearing, when i can be f**ked i go find one of my mechanical engineering books, and post up some facts about plain bearing and ball bearing...
Im studing mech engineering, so im tring to think like an enginer and i cant see how in this day and age a company that is there to make money would choose a option which doesnt meet the standards of say another company making a similar item (for example greddy and hks)
just my 2cents