If you are talking the 0-6-0 saddle tank locomotives, they are bullet proof. I have an old conventional one that I've converted to DCC. It has always pulled a ton of cars for it's size. The only issue I've had it the couplers. Due to their long arm length they break or bind easily, but then I ran mine on the floor where kids and cats are active. Once I replace the coupler and it stays on the layout I expect many many years of good service out of it. I might also get me one of the new LC+2.0 ones in the future to have two of them.
The old conventional ones are AC only out of the box. The LC ones should be DC or AC, but I've never tried to run LC locomotives on DC. I do not know if the LC+2.0 ones are DC as I have not read the manual yet, but you can do that as Lionel has them online. They do have DC motors, so you could remove the Lionel electronics and add your own, but opening and putting this little locomotive back together is a huge pain.
The short of it is I have no problem recommending this small scale locomotive to others to get. My only question to you is why are you running O27 locomotives on DC when they are all AC natively.
