"I've never used radar before, here in the Great Lakes, it's not that necessary "
I would argue that point. Here on the great lakes we have a lot of freighter traffic and other big boats like car ferries. Radar is useful. If you have it, learn how to use it and make the best of it.
Radar coupled with AIS is VERY useful on the lakes.
Now, as far as safety; People should generally not be within the radiation pattern of any transmitter. It's just good practice to stay clear. Even though the manufacturer states a 30 degree pattern, there are "lobes" of radiated energy outside of that normal pattern, but usually at an order of magnitude less power, so from an exposure perspective they are good to avoid, but I would not get too crazy about it.
If it is foggy and I am on the water, I will opt for the radar over worrying about the radiation risk. It probably is less exposure that you get every day in a city because of all the (hundreds or thousands) of sources in our every day life. If it is someday proven harmful, your greatest cumulative exposure is not going to be from your vessels radar.
The fact is, that freighter you did not see in time to get out of her way will very likely kill you very quickly. The radar energy.. well, it's not even proven to be harmful at normal levels.
I do however take issue with the comparrisson to a "Small Microwave". While that is technically correct, that definitely should not be a safety endorsement. Getting in front of that emmitter beam directly would be excruciatingly painful in a few seconds.
Use your radar, it's worth it. But as a fellow boater, even though I am not afraid of it, I would prefer you did not operate it at the dock or in ancorage where I am