I decided against them because they start on a particular date and assume the race is on a Saturday. They just didn't line up with my target date at the time. I chose MyAsics instead simply to have a plan customised for my target date.
Regarding intensity, so long as your current performance meets the requirements for a given plan, I wouldn't worry about it. It is counter-intuitive but easier workouts actually make you faster particularly at longer distances like the half. I'm not suggesting that none of your sessions should be hard but the plans usually factor in enough of everything. Remember the aim of the game is to complete all the training without sustaining injury and be fit for your race.
You might find some of the articles and threads from this site on HRM training interesting. I mistakenly used to think that I should be pushing myself really hard in every training session and the result was inevitably injury. Even when I finally understood that was stupid, I still didn't appreciate how low the intensity of an easy session should be for my body. An HRM helped me appreciate that.
Take a look at the RW book "RUNNERS WORLD RUN LESS RUN FASTER: Become a Faster, Stonger Runner with the Revolutionary First Training Program". I'm in the process of preparing to use one of the plans from it so I can't say how well they work but there are plenty of testimonials and research evidence to say they do. The plans are based on paces derived from your PBs and seem to have a nice blend of hard and easy workouts.
Good luck.
Edited: 22/11/2011 at 11:14