I must say I have not thoroughly checked all the available ebooks on the market when I made my mind up for a PB 912 a month ago. A mandatory feature for me was the ability to read PDF in a large screen, and to reflow their text : PB 912 can do all that. Plus : it's a rather open system, a feature to which I am sensitive, so I guess that's why I made it for a PB 912, but not really «over the Onyx M92».
For the «screensaver» feature you're asking for : yes, the PB 912 does that. Actually, it's more like a «power saver». It automatically shuts down after 5 to 30 minutes of inactivity (customizable parameter in the config menu), displaying a picture of your choice (or a random one within a folder) after power-off.