Just a word of experience -
I used to have one of those Reliance 10 breaker panel kits, and decided after one year of using it, and still running extension cords all over the place, I bought a Square D interlock kit for my panel, $45 bucks at Meynards, sold the Reliance panel on Ebay for $380.00, made a profit, and kept the plug. I noticed that these reliance panels are going up in price.
Just marked the hot tub and AC circuits with a red sticker to make sure I shut them off and no problems, nice to have the whole house with power.
The only regret is it was easier to tell when the power came back on with the reliance transfer switch, now I have to look at neighbors to see if it came on or not. I think you can buy some type of CT that you can attach to the main that will light up a light when the mains are back on, just haven't found an innexpensive solution...
This post is made with meat biproducts.