I bought the Rolls PPB 224 to supply 48v phantom power to my pics in the field. I am working on a recording project collecting nature field recordings from along the length of a river here in the UK. I need to power a pair of Rode NT1a mics as well as a pair of spaced omnis. I'm also using hydrophones.
The point of this review is to tell you that even when using the Rodes, with their very low self noise, the Rolls adds nothing I can detect to the signal.. it is dead quiet.
The down sides? None really. It is a little bulky if you're using a handheld recorder. It takes 2 P style 9v batteries rather than 1 but I bought some very long lasting rechargeable so should mean not changing very often.
I would recommend this product over competing products costing less. I have used one of those and it added audible hum to the signal path, which for my. Needs makes it not suitable. The Rolls is solid, well made, and above all audibly transparent.
Thomann provided me with excellent service and fast shipping to the UK, so thumbs up there too.