sight glass

Here's someone that will replace the plastic sight glasses in the master cylinders- http://www.ebay.com/itm/NEW-SITE-GLASS-MOTORCYCLE-Clutch-Brake-MASTER-CYLINDER-/370418875615?item=370418875615&pt=Motorcycles_Parts_Accessories&vxp=mtr#ht_4920wt_952

Anyone know anything about these: http://www.newrivercyclesalvage.com/sight%20glass.html Seen 'em mentioned on other forums. I'm gonna do more research over the weekend.