The following table shows the economics of saltwater chlorine generators and why they save money IF one uses a larger (often oversized) unit and is in an area where electricity costs are not very high.

Pool Size 18,000 Gallons
Power Cost $0.10/kWh
Name Model Output
(lb/24hr)
FC/hr Life
(hrs)
Power
(Watts)
Power
$/lb
Chlorine
New
Price
Labor Total
New
New
$/lb
Chlorine
Replace
Price
Labor Total
Replace
Replace
$/lb
Chlorine
Total
1repl
Total
2repl
Pentair
Intellichor IC15 0.60 0.17 10,000 65 $0.39 $460 $200 $660 $2.64 N/A N/A N/A N/A $3.03 $3.03
Intellichor IC20 0.70 0.19 10,000 220 $1.13 $720 $200 $920 $3.15 $455 $200 $655 $2.25 $3.83 $3.68
Intellichor IC40 1.40 0.39 10,000 220 $0.57 $787 $200 $987 $1.69 $513 $200 $713 $1.22 $2.02 $1.95
Intellichor IC60 2.00 0.56 10,000 220 $0.40 $995 $200 $1,195 $1.43 $770 $200 $970 $1.16 $1.70 $1.65
Hayward
AquaRite T-CELL-3 0.60 0.17 7,560 150 $0.90 $655 $200 $855 $4.52 $219 $200 $419 $2.22 $4.27 $3.89
AquaRite T-CELL-9 0.70 0.19 11,800 150 $0.77 $765 $200 $965 $2.78 $335 $200 $535 $1.54 $2.94 $2.72
AquaRite T-CELL-15 1.45 0.40 8,640 150 $0.37 $845 $200 $1,045 $2.00 $409 $200 $609 $1.17 $1.96 $1.82
AquaRite T-CELL-15LL 1.45 0.40 10,577 150 $0.37 N/A $200 N/A N/A $641 $200 $841 $1.32 $2.03 $1.92

The unusual cell lives for the Hayward cells are calculated from this document where they list "equivalent pounds of Trichlor produced over the lifetime of the cell" where I assume 90% Available Chlorine. So, for example, 0.9*210/(0.60/24) = 7,560.

The above does not account for the cost of salt which for an 18,000 gallon pool would be 450 pounds of salt (if starting with no salt and getting to 3000 ppm). Morton Pool Salt at Walmart is $6.38 for 40 pounds so 16 cents per pound. This is $72 so not that much compared to other initial costs and maintenance. I am also not including the cost of acid that usually needs to be added to the pool. That could be as much as $15 per month if the pool isn't managed well to reduce this need, but people can usually get this down to $6 per month or less. This acid cost is significant since $6 per month at 1.5 ppm FC per day for an 18,000 gallon pool is roughly $1 per pound chlorine (i.e. increases the above numbers by $1).

Note that the cost for chlorinating liquid or bleach is usually $4 per pound (chlorine gas equivalent) or less and Trichlor is about the same price but requires a base as well. At discounted prices in some areas the chlorinating liquid or bleach might get down closer to $3 per pound or even less when on sale. For reference, 12.5% (trade) chlorinating liquid at $3 per gallon is $2.88 per pound; at $4 per gallon it is $3.83 per pound.

So it should be very clear from the above table that to get significant savings one really has to use the larger cell sizes of the IC60 (or at least the IC40) for Pentair Intellichlor and the T-CELL-15 (not LL) for the Hayward AquaRite. This assumes that the cells actually last as long as indicated based on usage and that they do not degrade at all based on time alone. [EDIT] Note that the larger cells will output higher FC out of the returns (see this post) so for lower pump flow rates and/or smaller pools that could be too high an FC. [END-EDIT]

Note that the economics change considerably if electric rates are high. Instead of the 10 cents per kilowatt-hour I used above, if I assume 40 cents per kilowatt-hour then the IC60 cost is $2.85 assuming 2 cell replacements before the entire system needs replacing while the T-CELL-15 cost becomes $2.93. Add in the cost of salt and especially acid and this may get to roughly the same as or more than chlorinating liquid or bleach.

What has changed over time is that the life of these cells has increased so they are more economical now than in the past. Note that at 2.0 ppm FC per day in 18,000 gallons, the IC60 lasting 10,000 hours in theory would be able to operate for (10,000 hrs)/((2.0 ppm FC/day)/(0.56 ppm FC/hr running)) = 2800 days or many, many years (over 7 years if used all year long).

I made assumptions for labor for installation and cell replacement maintenance at $200. In practice, many people don't buy their equipment at the discounted online prices I show above and instead the installer charges retail and pockets profit from it and charges labor on top of that. In that scenario, the economics will be a lot worse than shown above.