I haven't tried that part... my only external RTC usage is in old products that were designed some years back. I almost certainly won't go that route for future projects. The reasoning for that being...
(1) Most 18F Parts for example have heaps of spare capacity - both in program space and performance.
(2) You can select a micropower part that doesn't suck a lot of juice
(3) With little effort you can redesign your PSU so that it powers the PIC all the time, whilst powering-off the remainder of your device, so the PIC remains quiesced on just minimal residual backup Battery Power.
Ultimately the name of the game is to reduce the parts count...
(a) Removes the cost of the parts (which considering an RTC is half the price of a decent PIC doesn't give you a great deal of bang-for-buck).
(b) Makes the PCB smaller (thereby cheaper)
(c) Removes the Labour cost involved in mounting the parts, in ordering the parts and in inventory.
(d) If it's the only I2C device, you lose two pull-up Resistors as well.
Eight or even six years ago, the state of electronics was such that your microprocessor needed all the external help it could get. This has changed. Today, you chose the part that could do as much of the job at hand that you can possibly make it do. There isn't the budget for unnescessary extravagence - you need to leverage maximum profit and in so doing need to think clever.
Today if I have a production run of say 1000 pcs of a new product needing an RTC, I can earn an extra $750 in return for two hours worth of programming - I'll do it. Wouldn't you?
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