The orrible concave platter is a clever idea from Oracle.

Originally, Oracle had a flat rubber platter and used a small middle high piece at he spindle, so that the screw down clamp would effectively make the record perimeter better touch the platter... This system somewhat worked but cracked many a record center hole in clamping down the record.

The slightly concave platter mat means that the record perimeter sits very well on the perimeter of the mat. The center of the mat is just a little lower, so that the record clamp can easily & better mate the record to the mat/platter. Also the mat is made of Delrin. Delrin is a very popular material used in turntables and is also used by Clearaudio.

The only other alternative to bond the record to the mat is a record ring sold by TT Weights and also VPI and others. I have a record ring and its sonic qualities are worderfull – but it’s just an extra procedure I seldom do.

Mind you, most platter mats are flat, and flat is far from ideal for the record to properly mate to the platter, unless we are mostly playing higher priced audiophile heavy records…

So a concave mat, while sounding orrible to some, may be worth consideration…