Unless you are preparing for a deeper dive or doing this as part of a class, for dives to 130 ft or less, there is really no need for 2 deco bottles. I would have to agree with the "Great Bartman" on this issue that it is better to reduce and minimize.
Now, to back my statement up I just plugged in to my handy smart phone, dive computer a 60 minute bottom time at 130' on Nitrox 28% with a 80% bottle for deco beginning at 30'. The total run time is 111 minutes. Same dive with additional 50% picked up at 70' only reduces runtime to 104 minutes. Many divers are not doing 60 minutes of bottom time at 130', but those that I know that do this regularly, are only using 1 deco bottle. If you do that same dive on Air for the bottom time, with only the 80%, it increases the bottom time to 130 minutes. I don't see the logic in using Air over 28% because on these long dive, it saves 19 minutes of deco time. I also don't see the logic in using Air and then paying for 2 deco bottles when you could have just payed for the 28% and 1 deco bottle fill.
Anyway, just my 2 cents based on years of diving. And I don't claim to be a genius.
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