Not actually rare, I got scrammed by 1-2 anchoring Demaviks in every Conduit I ran for test purposes on SiSi. There are so few sites, you have little chance to find one on TQ which is not sealed.
The sites work like FW sites (anomaly -> beacon) and have three waves of increasing difficulty. You can solo them in a T3 (took me 20min in my Loki), but this is theory, as you won’t be alone for a sec on TQ, because of the sites’ scarcity.
The payout is max 15M and decreases with more people in site doing damage. Not sure when the payout goes down. Texts I read suggest above 3 people. You can loot more valuable stuff from Zorya’s ships, if you are lucky.
The gameplay is more like the old events, than Incursions. But with the very limited amount of sites (4-5 sites every hour per Invasion, makes a total of 15 sites in New Eden), no option for income.
BTW, you should deal explo, and tank against therm.
BTW2, you can warp freely in sites which helps with tactics.