I don’t know about cheaper to run, have you looked at the energy tags in new fridges?  Even the humongous  33 Cu. Ft models cost about $60 a years to operate, using a national average electrical cost. Even if you saved $40 a years that is less than $2/month, really nothing.  I'll take the space over the savings.

When I this apartment apartment in 1997 I Though "Only my mom and I" So, Why the hell would we need a huge standard size dishwasher? So I bought a countertop compact dishwasher (6 services) from Brastemp.

That was one of the worst calculation mistake i made in my whole life. I forgot to consider my father (they are divorced) 3 sisters and 1 brother that come to eat here every day. The family grew up less than one year later (2 brothers in lar and 1 sister in law.
Then the family grew up even more... my brother and two of my sisters had babies almost at the same time. 

I bought a second compact dishwasher from brastemp. My sister bought it 12 years earlier and it was still in box.

Not satisfied having to wait for them to finish the cycle to unload them and load a third and sometimes even a 4th load, I got my third compact dishwasher last year.  This time, an Electrolux.

I was impressed by it's performance and design.. It's shorter and wider . Honestly I always saw that machine on the stores and I had the impression it would be terrible with only one rack. And it uses so less water and electricity than my previous machines and it cleans much better because it has only one spray arm so, there's even more pressure on the jets.

About a month ago, the first dishwasher died after 17 years of good work. I would have been easy to fix it but I didn't want to. As my brother died, one of my sisters god divorced and now with my mom sick (Alzheimer's) they don't come visit too often.

Only two dishwashers are being ok here. I'm using only the Electrolux every day and the Brastemp only sometimes.

Yesterday night there was a dinner party here to celebrate my birthday. 15 guests.

I bob loaded the Brastemp right after the dinner and before the dessert.  When the last guest was gone, i loaded the Electrolux (another bobload) and the Brastemp was ready to be unloaded. I did it and loaded the pots and pans and went to bed with my kitchen sparkling clean. Nobody would guess it looked like a war zone a few hours earlier.

Nowadays, If i had to buy appliances for a new kitchen, I wouldn't think twice before getting two of these Electrolux compact dishwashers instead of a full size model only to have this flexibility. Two of them would give me exactly the same capacity but the flexibility of using only one if I don't have too much dishes to wash.

But also, one thing to be considered is the price. I'm not sure but in the US, it seems that the compact dishwashers are expensive or almost the same price as a standard size dishwasher. Here in Brazil most of the dishwashers are compact (and much cheaper) than a ful size dishwasher. Getting two of them would cost less than only one full size.