MTBF (Mean Time Before Failure) is a fairly meaningless statistic in this context.
Supposedly, it is similar to the average lifespan of the product. To take the 120,000hrs quoted...
120,000 / 24 = 5000 days
5000 / 365.25 = 13.7 years
Therefore, the DVD would be able to play continuously for 13.7 years? How on earth did they (sensibly) arrive at that figure? And who on earth is going to try to prove them wrong? And if one should fail after 1 year, does the next one off the production line last for over 27 years?
Access time on a drive is the average time taken to move from one part of the disc to another, e.g. from track 1 to track 2. Slightly more useful, but due to the way that the information is buffered (held in memory), the buffer is always full enough to compensate for any slight pauses while the drive head moves from track to track - you won't notice any pauses.
Any DVD player will be able to play CDs - it's part of the specification.
The simplest guide I can give is - find a DVD player at the price you can afford, and type the name and model number into Google, with the word 'review'. If it has a problem, you will find out, although they are few and far between.
The fittings are just the same as for a CD player - 4 screws to hold it into the case, a connector for power, data, and audio, plus a set of jumpers to allow it to be fitted as a Master or Slave.
The only DVD/CD combo devices you might find are those that combine a DVD player with a CD Writer, or even more rare, a DVD writer and a CD Writer in the same unit.
The fact that manufacturers and suppliers need to resort to such relatively meaningless statistics as MTBF and access time, should illustrate that there is so little to distinguish one model from another. Hence the standard marketing fallback of trying to produce a feature list that is longer than competitors 'the bigger the feature list, the better the product' - wrong!
The only slightly advantageous feature is playing speed. Once software companies start routinely releasing software on DVD, a faster playing speed will allow a programme to be installed from DVD a few seconds quicker. Not really worth spending a lot of money on, in my view, unless you are installing software from DVD daily.
Hope that clarifies, rather than confuses :)