The pipers being regrinds use the metod of reducing the BCD (base circle diameter) to increase the relative lift value from the centre of the cam. However, because they reduce the BCD the radius followers pivots have to adjust to take up that extra clearance, and they just dont have the scope to do so by the amount needed. Hence the followers do not sit on the cams lobe surface all the time and a clearance value is achieved (they should run zero all the time). The slack is taken up by the flank of the cam lobe, as it hits the follower at a rather high rate of speed it creates the tap noise.
In my opinion its bad because of a few reasons. The clearance that they have means that the valve experiences an initial acceleration rate much higher than std or even properly designed wilder cams. This will, IMO, over time have a bearing on the valve stem tips becomming damaged as even 10 thousands of an inch can double the speed at which the tappet hits the valve stem. The other reason is that the valve acceleration rates are higher and more aggressive, leading to less dwell at peak lift, and more potential valve float and bounce as there isnt a nice gentle lead in and out of the ramp for the follower to slide along.
For this reason my cams have the largest BCD on the marketand ground from blanks, and are the most gentle on valve train assembly, whilst having the most lift and generous duration, eventhough the valve events are conservative.