You might be better off with an aerator and aerating the crap out of it with multiple passes. You need seed to soil contact and you can only set a slit seeder so deep die to the fixed tines. If you have a riding mower with a hitch you can get a tow-behind aerator. A dethatcher has flail-type tines that you can set deeper and sort of do a shallow tilling. A slit seeder wood be low on my list for using to renovate an uneven lawn.Interesting - I hadn't seen those two. Have seen the Lesco, Classen, and Billy Goat ones.... I think I only have access to Lesco Renovator 20 or Classen TS20. Hard to tell which would be better - was going to go off name alone and try the Lesco I guess. Tiny chance i can get a Billy Goat which looks better for uneven ground - kind of pivots in the middle so the cutters track better it seems. Need to call one place in the morning. I think the lesco does have a brush behind like those you mention.
Sadly my yard is the definition of humpy lumpy bumpy and way too big for me to ever level out. I'm just going to give it the best shot I can to thicken things up to keep the weeds down - I have terrible weed pressure on 3 sides of unmaintained yards I think it's thin enough so I won't have a substantial amount of thatch come up.... I can see dirt between the grass blades in most areas still.