As a major point in their favour, at least they kept the old version. They could have just redesigned the webpage and put it on i.reddit.com. Instead I can keep using the same good old layout while those who want can use the new m.reddit.com.
That's more than I can say for many, many other things, where whether I like it or not I'm forced to have the latest design fad (flat, pastel colours, long and inefficient animations and huge, unnecessary padding nowadays) shoved down my throat.
I know nothing about this, but there's a flag on https://m.reddit.com that says "Beta", and on https://i.reddit.com there's a link to "try the beta", so I think it remains to be seen whether the old version is still available when m gets out of beta.
I also don't understand the redesign. The old version is way better then the new version, but I guess it just does not look flat and material enough.