I am a fan of BEX, don't get me wrong, but I dare you to ask Symantec or Microsoft if BEX's brick level backups are fully supported by Exchange and guaranteed not to cause latent corruption. Personally I wouldn't use it and would stick with the recovery storage group restore method, even if it takes a bit more time.
The advantage of DPM is that is ONLY uses approved backup methods. Yes, it is more limited to Microsoft-based products (or rather products that support VSS). And Microsoft uses DPM exclusively at their corporation which includes tens of thousands of servers. Don't know where you got the idea that it is only good for sub-10-server environments. It also supports any tape drive that appears in Windows Device Manager.
That being said, it is not necessarily as good as BEX at some things. I prefer BEX for server recovery (not BMR, but doing a full restore of the OS partition, system state, etc). DPM doesn't do that very well at this point.