I thought I should update my experience with this adventure. I ended up staying un-amped.
The cable goes from the antenna in the den window to an unpowered splitter. The splitter goes to the 2-tuner tablo and 2 tvs. After extensive testing (watching a lot of TV), I have found no noticeable loss of quality with this set-up.
When I connected the pre-amp(s), I tried both:
I performed this testing during the afternoon (well before sunset) on a clear day (almost no clouds visible). I checked the weather forecast as many of the towers are quite far away 30 miles or more.
Several channels disappeared during a channel scan. These were the ones that had the best strength to begin with. I expect the amp was over-powering them and overloading the tuners. One new channel showed up. I wasn't going to watch anything on that channel anyway.
Most of the poor signal strength channels showed up and had stronger signal but were still showing corruption during testing.
Without the pre-amp(s):
With both TVs and the Tablo (2-tuner) connected, I lost one channel I wasn't wanting to watch anyway. All the other channels, even the ones with mediocre signal strength, still come in and don't seam any worse.
There is occasional signal corruption in the form of very short bits of images becoming blocky. It reduces when overcast but increases during bad weather, so I assume this isn't related to cell-phone signal interference.
I'm sticking with un-powered. I'm keeping both of the pre-amps. The cheaper one I can't return (I checked). Well, I could but the "restocking fee" is almost the same as the cost of it. The expensive pre-amp is a good one (channel master) I got on sale. When/if I move, I may need it.