I have exactly that model - LWB SE '07. First off, the SE is quite rare compared to the more usual 'Sport' models. No real differences mechanically. The SE usually comes with real leather instead of half suede half artico leather and the interior colour choices are different e.g. Sports are generally black or dark grey inside whereas mine has Cashmere leather and brown wood inserts instead of dark/black wood or chrome inserts.
I have had mine for 5 years and have had hardly any issues with it. I had an oil leak in year 1 and a replacement alternator in year 2, but apart from that it has been brilliant.
Brilliant on the motorway, very comfortable, smooth etc an pretty economical 30+ at legal speeds. Around town, although it is a huge car, is easily manageable.
Super practical, loads of space. Amazing value for money, now starting at less than £10k.
I still love driving mine everytime I get in it, and I have never kept a car as long as I have this one - for me at least, I have always thought of the R Class as 'almost' and S class estate!
As you can see, I would not hesitate to recommend them - just make sure you get the LWB as the SWB doesn't seem to make as much sense to me.
Good luck, and happy to answer any questions you might have now or in the future.
If you are looking at a particular car - let us have the link to the dealer website or the autotrader link and I'm sure there are plenty on here who would be happy to give you our thoughts!