Just be aware of the difference between an "approved" oil and an oil that is "recommended for use in..." or "suitable for use in..." or "meets the requirements of..." etc.
Take MB229.5 for example. This is a specification document that defines what physical, chemical and performance properties an oil must meet in order to be certified as appropriate for use in the relevant Mercedes engines. It contains over 40 data points for lab testing and 9 separate engine tests, some with up to 20 individual parameters measured, rated and reported. The engine tests cover sludge formation, wear, fuel economy, aeration, LSPI and fuel-induced deposits. To run all of these tests to qualify an oil costs a lot of money and takes a lot of time, and there's no guarantee of hitting each one first time, so some tests will have to be repeated on reformulated candidates. Once you have a full suite of results that pass every required limit you apply to MB for an approval and, assuming they accept your data, they will officially record the oil as approved, send you a letter to prove it and put it on their BeVo database for everybody to see.
Some oil companies go through all this time and expense and get the letter. Some others don't - they will make a judgement based on testing they have carried out, or based on knowing what's in their oil and how it performs, and will effectively underwrite the specification themselves. The only people who know how the specification requirements relate to engine reliability, performance and durability are Mercedes and the only way to know that an oil meets MB's demands is to hold the official approval.
Once you start comparing oils that are on the BeVo list then you're into price, availability and perhaps any other performance benefits that the oil supplier may feature. One thing about specifications is that they often only give a maximum or minimum limit for a test result - this is like a high jump competition; if you clear the bar you pass, regardless of whether you just brush over it or whether you clear the bar by a good margin - you get no additional merit in terms of the approval if your result is a stellar one. However, the oil company will have the results to hand and may choose to call out any particularly good results such as "x times better wear" or whatever. It's up to you whether these additional factors are valuable to you.
And let's not forget, in many cases an oil has not only jumped the MB high jump bar, but also other bars from, say, VW and BMW - and in order to qualify for these high jump competitions at all you have to qualify at the ACEA prelims - another specification standard that underpins all of the European OEM specifications.
So, oil isn't oil - there is a lot that goes on in the formulation that differentiates one from another and defines which applications they are appropriate for - this is why there are so many products, even from the same supplier. Fundamentally there's an old adage - "any oil is better than no oil", so using the 'wrong' oil is (in most cases) unlikely to be catastrophic, although as emissions control systems become more complex and common, even this is not a given. But even if not catastrophic, the results may be incrementally worse.
The only way to be sure is to use the appropriately specified and approved oil. You may get away with it outside of that safe zone (and many have), but you're on your own. BITOG is a (largely US-focussed) forum where such experiences are shared.
.
