I have had a number of electric pressure cook brands over the years, and the Ninja Foodi pressure cookers with the air crisp lid is my favorite. First of all, to me, it doesn't make sense to buy a 6 quart pressure cooker since the quantity you cook is limited to the capacity of the cook. With an 8 quart pressure cooker, you can as easily cook smaller quantities as larger ones. I always opt for the larger size since cookers I have had in smaller sizes were never used.I also have had the Ninja OP301 pressure cooker with the air crisp lid for over two years. I use it almost every day and it still works and looks like new. I like it so much, when I saw the Ninja FD401 unit on sale during the Amazon Prime days, I jumped on it. I wanted an extra in case the one I have fails. From experience, I have learned this usually happens in the middle of making dinner.I have looked into the differences between the two units, and I'm not sure whether I prefer the OP301 unit to the DP401 unit. The OP301 is describes as a 9-in-one and the FD401 is described as a 12-in-1. The OP301 actually has 7 cooking functions to choose from and the FD401 has 8 functions to choose from. Some functions are combined to come up to the 9-in-1 for the OP301 and 12-in-1 for the FD401. The following is the differences between the two units. - Cooking functions - The FD401 added Yogurt to the Slow Cook function. OP301 - Pressure, Steam, Slow Cook, Sear/Sauté, Air Crisp, Bake/Roast, Broil, Dehydrate FD401 - Pressure, Steam, Slow Cook/Yogurt, Sear/Sauté, Air Crisp, Bake/Roast, Broil, Dehydrate - Cooking function selection - The FD401 uses the Start/Stop knob to scroll through the functions for selection and to increase or decrease time and temperature. The OP301 has buttons that can be pressed for each function. Personally, I prefer the selection buttons on the OP301 to the dial used for selection on the FD401. - Time and Temperature - On both units there are default settings for both, but time and temperature can be easily changed on both by pressing the up/down buttons on the OP301 or using the dial on the FD401. - Accessories - Both come with the same accessories: reversible rack, cook/crisp basket, etc.I use my Ninja Foodi almost every day, and bought a couple accessories to increase the uses . Since I grow a number of veggie greens in my basement, I bought a steamer basket from Amazon for an 8 quart pressure cooker that I use to steam the veggies. The thicker leaves require 8-10 minutes of steaming, and the thinner leaves, like spinach, require only 2-3 minutes of steaming. I also bought the Ninja Foodi Skewer set that works wonderfully for cooking and browning BBQ'ed chicken wings, chicken thighs, and brochettes using chicken, fish, shrimp, or beef. The air crisping lid is used for the chicken wings and thighs after cooking them with the baking function.As a pressure cooker, this Ninja Foodi saves so much time, and the results are always wonderful. For example, a pork shoulder roast needs to be pressure cooked for only 55 minutes, and the liquids left make a wonderful gravy. To do this, put 2 cups of beef broth in the bottom of the cooking pot, add 1 large onion cut into wedges, 5-6 garlic cloves (or to taste), and seasonings. After the pork shoulder is done, remove it and cover with tin foil to keep warm. Set the cooker to sauté low, use in immersion blender to blend the onion and garlic, add a mixture of 1/4 cup water and 2 tbsp. corn starch, and cook until the gravy thickens. Using the pressure cooking function, I have also made pot roast with potatoes and carrots, corned beef and cabbage, short ribs, beef stew, and more. All have come out perfect, and all were done in 1 hour or less.In conclusion, both units supply basically the same cooking functions, and both are excellent cooking appliances with multiple cooking functions that will enhance the cooking abilities of anyone using them. Personally, I prefer the button selection of the OP302 over the FD401 unit simply because pushing a button for the desired function is much easier and faster than scrolling to the desired function with a dial.As for storage of the Air Crisp lid, there is an option available on Amazon to store this lid on top of the pressure cooker. I have this, and now store my Air Crisp lid on top of the pressure cooker.Another important point to mention is that many of the newer appliances use wattages from 1500 to 1800 watts. This unit is rated at 1760 units. We have a 40 year old home and most of the circuit breakers were 15 amps. This could handle 1 appliance if nothing else was running at the time of the appliance. I was having a problem with circuit breakers popping when using two appliances at the same time and sometimes when I was using only one. This made cooking dinners very frustrating as the cook times were lost when the breaker popped. We finally had an electrician come to the house to upgrade our circuit breakers to 20 amp and many of the outlets in my kitchen were wired to separate circuit breakers. This made dinner cooking a lot easier for me, but it came at a cost of over $3000. If you have only a couple of the newer appliances, including this one, you may have a problem if you have 15 amp circuits and anything else is running on the same circuit at the same time.I hope this review was helpful for you. I will update my review if my opinion changes or I can add more information.