Great post. There's a lot here to discuss.
Wave Kinetics, Dobbins Beat, Technics SP10s, Basis, SME, Brinkman, TW Akustic, to name a few, do not design tables with periphery rings. And a few vinyl aficionados actually prefer smooth metal platter surfaces with no clamp, no rings or any mechanical means to flatten LPs. (I often wonder if the LP slips due to stylus drag, but that is for another thread).
Based on what I have seen with my turntable, I don't believe the record slips due to stylus drag, but it does slip a bit at start up, if you change records on-the-fly. I don't know if there is any record damage due to metal platters because I chose an acetal surface. I did that because I like how it mates with the record from a resonance standpoint, and because it is a "vinyl friendly" surface that won't scratch records. The downside is that it can pick up abrasions easier than metal. I have a workaround for OCD guys, but I don't worry about it for my personal use. Anyway, a solid surface is less lossy than the alternatives, in my opinion.
I once tried to buy an LP on Ebay and the seller contacted me to cancel the sale because he noticed a severe edge warp that his own tonearm would not track. I really wanted to buy this record, so I offered to buy it without a return policy at a dramatically reduced price. Once it arrived, I did notice a severe warp. My table tracked it without incident and without the need for a periphery ring.
A good tonearm with a properly aligned cartridge struts its stuff on marginal records. Fortunately, those who pay thousands for turntables generally insist on flat records. I have found a cheap puck to be useful at times, though.
I agree that rotational mass increases with the addition of a periphery ring, but it does not necessarily follow that the speed accuracy and/or consistency improves or even remains the same. I think this would depend on the motor's torque, the drive type, and perhaps other factors. If the motor's torque can not handle the added mass, the platter should slow down and the speed may need to be adjusted.
A periphery ring shouldn't affect anything with a turntable that was built employing a "brute force" principle. I don't know any modern turntables built that way, though. The EMT927, Fairchild Studio 750, and the old Russco models come to mind as ones that do. Of the modern turntables, the better designed ones use managed torque implementations that factor in inertia as precisely as possible. They are balancing acts that are hampered by anything that upsets the proverbial apple cart, and periphery rings certainly do that.
Some tables don't offer speed adjustment, hence my question of whether or not anyone has observed the effect of adding a periphery ring with a speed checking device like the Timeline or even the KAB strobe. I have tested a turntable with a periphery ring with my Timeline, and it was very slow. The owner claimed that the use of the Timeline is a flawed testing method. We did not try to increase the speed to see the effect on platter speed with and without the ring. He assured me the speed was correct, so we moved on to listening to music.
If that owner was saying the Timeline was flawed as an excuse for his table running slow with a ring, he is deluding himself. Of course, it was slow. The Timeline is extremely accurate for checking average speed. Where it and strobes fall down is that none of them can tell what is going on during a specific RPM because they only measure the whole RPM. If you have a turntable that constantly hunts and corrects due to a poorly designed speed control, none of them will tell you. The micro dynamics of music will, however. They won't tell you if the platter slows down or speeds up when it encounters transients in the grooves, either. Your ears will, though. You may be lulled into thinking the music is great, but an A-B with a good turntable will quickly change your mind.
The Timeline is great for setup. That's where it excels. I use a KAB strobe, and follow up with a Timeline. Then, I lock the speed at the controller. I have found that method the best way to get the speed dead on.
That's my opinion...for whatever it's worth.
