We purchased from Costco, the Firman 7500 Tri-Fuel. It was a DIY project. It sits outside full-time, in a DIY shed that conceals, protects, adds greatly reduces noise. Wired directly to the service panel with a throw switch. Natural gas is my normal fuel but have backups. I like the electric start and start it each month to keep the battery charged. I also had a slow-starter added to the air conditioning so 7500w will start the unit with no issues. It's a poor-gal's Generac except I don't have auto-detection-and-start or the fancy diagnosis.
I've had to use it 2 or 3 times a year for, usually, winter/spring power failures. I run it 2 hours in the morning + 2 hours in the evening to return the house/freezers to temperature, do laundry, cook dinner in my regular kitchen and recharge batteries.
The Batt-Mobile is another DIY project on the cheap: a sturdy tote with Faraday protection, on wheels. Inside are 3 100amp marine, deep cycle batteries (yep I know, I need to upgrade them), a 3,500w inverter and various plug-ins. This runs the security system and home office, or whatever when off-grid. It's re-chargeable via A/C/gen or 800w solar. In my area, 800w solar will fully recharge my batteries in about 5 hours in summer but not in winter.
The combination seems to work well for me. I like the redundancy. The real key, IMHO, is to have a power-use plan when off-grid.