There is another thread on this site that discusses the PP5 (on the Road Bikes section) to which the great GP Lama himself contributes. Have a read..
There is also a recent Tom Bowers cycling review on YouTube as well.
His experience was the same as mine. There are limitations, but it is perfectly possible to work within those. The GP Lama residual torque issue would be a massive ball ache if you were doing sprint training or microbursts, but for a casual rider or even a time trialler that doesn't have spikes in power, it should be good enough. For me due to a L/R balance that doesn't stay consistent- it is infinitely superior to any left side only device.
And for $69, as long as you don't also need a new crankset to fit, well worth trying to make up your own mind.