I'm a happy telerik customer for more than 5 years. I used their ORM only in one solution and never used an open source ORM.
Throw away the existing one?
NO - if you have no problems and the thing does what it should do I wouldn't change.
That has nothing to do with quality or other asspects of telerik ORM.
It's just a matter of fact that using a new product means to learn new things, solve some solved things again in a different way and so on.
BUT - if you have problems (or must make compromises) with your current product it's sure worth to give it a try.
Without knowing other ORMs I have one clear point why I would try telerik ORM.
It's their (telerik's) outstanding support.
None of my other vendors offers / does what telerik does.
Simply take a look at their forums http://www.telerik.com/community/forums.aspx and you'll see what I mean.
You have a problem - they solve it; and that with very fast response times.
And that's a point you should think about when making a decission about ORM (or any ohter kind of product).