I've seen the Volvo counter display at the dealer parts window where they cut and cross sectioned a Volvo oil filter, Fram, Purolator, and Wix filters (there was about 6 different ones). The add simply pointed out the greater filter area, pleat design, flow charactreristics, and special one-way valve that the Volvo filter had compared to the others. All of these differences were obvious to see why the Volvo filter was superior and well thought out.
I've been buying nothing but Volvo filters since.
That was back in the mid-90's, so things may have changed since then, and the Mann has been considered a direct replacement, although I have not seen one cut away or flow tested. It may or may not be the same.
The main points that I see here, is that Volvo went a considerable distance to increase the filter area to improve oil flow and lessen the pressure drop across the filter at low flows, like idle or slow driving where engine temps are high. The valve and it's placement also keeps oil in the filter whe the engine is off, but is not a restriction to flow as is others that have a similar valve.
For the difference of $5, there should not be any question in your mind on which to use.
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'89 245 sportwagon, destroyed by hit & run driver, RIP. '04 V70 2.5 T Sportwagon, 12k mi and '91 245 5-speed, 209k mi, replaced the '89