Well, they're only 6 gallons, which is really too small even for 5 gallon batches. Otherwise, it seems like they would do. I'd get two of the ones with spigots, myself.
But really, I'd recommend getting some kegs and converting them so you aren't restricted to 4 gallons or so. Or check ebay for cheap stainless kettles. The spring lids on those boxes won't be particularly helpful, though the spigot is a must.