Thanks, we do lots of generators around here so it is a common question. I usually tell homeowners looking to have transfer equipment installed that, if this is a manual system, the listed panel interlock is usually the best way to go. The labor will be much less and the part, although ridiculous for what you get, is still pretty cheap.
The only thing they really need is a vacant double slot in the panel and moving some breakers around to get your backfed breaker next to the discionnect. You then have to be sure they lift the bonding jumper in the generator to get circuit current off the EGC. This will not be an SDS.