I've actually used that calculator to train for a 50K Mike. It got me to finish just fine. I never followed it exactly, but tailored it to my experience/time. But I think as a rough outline, it's a good start.
It seems to be a pretty standard buildup, typical of most programs I've used/looked at for distance (Jeff Galloway, Hal Higdon, Bob Glover, etc.). Roughly +10% volume per week, with a step back "rest" week every 3 or 4.
Most plans of this length assume you already have a base of at least 20-25 MPW. I've seen 50 mile plans with a more volume than this, starting at 35 MPW and peaking at 70-75 MPW, with longer long days. But I'd wager this is sufficient if you stick with it.
One thing it doesn't address is specificity. I'd certainly make sure to get in plenty of vertical on the Saturday and Sunday runs, as well as making the midweek "medium" run a "pace" day…either running it somewhat faster or getting in more hill climbing.
Conventional wisdom is to do your long days slow, and your medium days at a faster pace. One short day could be substituted for speed work or hill repeats…but most coaches I know argue that if you're new to running, speedwork/repeats might be a little stressful and you're better off just getting your body used to logging regular miles for a while first.
It's not really different from the way I have typically built up, though all my experience so far is mostly in the marathon to 40 mile range. I usually follow the same weekly schedule as in your link, only I vary the mileage a bit. I'll also make Monday a swimming day and mix in pushups, pullups, situps, etc. throughout the week. I've always kept 1 day for pure rest…for me it's Friday, usually the day before my longest runs.
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And then there's the other timeless training method:
Run, a lot, on terrain similar to what you want to race.
