The item is excellent!!!
The spin-on oil filter adaptors sold in the UK for TR5/6/250 Innsbruck 2000/2.5PI /GT6 etc fit to the block in place of the orig oil filter housing assy and turn the oil filter through 90 deg. so it hangs down, rather than being bolted sideways to the oil gallery. This means the oil filter is full of oil when you start up, rather than part drained. This eliminates the 'death rattle' as the engine starts.
Here is a photo from the Moss Europe catalogue pages of TR6 - the item shewn is with oil cooler adaptors.
http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=6961
And yes, a filter with a non return valve incorporated makes good sense. Get the right sized filter or it will hit your LHD steering column.
Oil filter change is so much easier and a lot less messy with this spin on conversion kit -
You still have to drop the oil out the sump plug though - unless you employ some suction arrangement to get the oil out through the dip stick tube.
Hope this helps
Peter W