https://multibit.org/en/help/v0.5/help_whatIsTheTransactionFee.html
There is a more detailed discussion upthread around about this post:
https://bitcointalksearch.org/topic/m.2603208
I recommend keeping up to date with the MultiBit releases to get the benefit of bug fixes and various updates.
For instance, in 0.5.13 there is improved wallet backups. This took me about a month to implement. The backup files are described in detail here:
https://multibit.org/en/help/v0.5/help_fileDescriptions.html
You can get this month's work for the price of $0 and 1 minute of your time if you upgrade to 0.5.13.
There has been at least one instance where a user has lost bitcoin due to a combination of what he did and how the older version of MultiBit he was using operated. If he had been on a more recent version there would have been bug fixes and extra functionality that would have meant he would not have lost his private keys.
Ultimately it is your choice what version of MultiBit you use. They are your bitcoins and you own your computer.
However support works both ways. If you don't spend a minute of your time to keep up to date you cannot realistically expect other people to help you if you encounter a bug/ problem that was fixed months ago.
I understand what the fee solver tries to accomplish and that you do contribute a valuable service to the bitcoin by continuing to develop improvements for what is the best bitcoin client for many use cases.
My predicament with the txfee solver using the new minimums is that, I most cases when I am sending transactions I want them to be confirmed fast which means I want to pay more than the default fee. Maybe for most users this isn't a very big issue, but for me being able to control how much of a fee I attach is a tremendous benefit of pre-5.12 versions.