Should I order open access if I've got the money?
Springer Open Choice, aka. open access, is the "new" way to publish things. In the traditional model, the journal publishes the paper, and then charges readers a subscription fee to read it. With open access, the paper is freely available, but the authors have to pay the publisher to publish. Copyright in OA articles are generally retained by the author, and there is no print version.

Springer's webpage gives you the advantages of doing it:


It makes your paper freely accessible.
It increases citation counts &amp; usage statistics. Note this is controversial. There's no doubt that open access increases usage statistics, but citation is a separate story.
It complies with funder mandates. If you're unfamiliar with open access I'll guess that your funders (if any) don't have require you to publish open access, so this is irrelevant.
You retain the copyright (if it matters to you for whatever reason).


There's really only one downside to open access: you have to pay for it. It's possible you have funding to do it (per point 3 above; also check with your library/supervisor if applicable). Otherwise there's the paperwork you have to do, and finally there's the danger intrinsic to open access. OA motivates the publisher to accept as many papers as possible (they make more money), which generates a conflict of interest. In your case you should be clear because 1) it's a hybrid journal, the offer of OA is only made after your paper is accepted + you don't have to take it up, and 2) it's Springer, which is a well-known publisher. But if you keep publishing OA then you'll inevitably encounter so-called predatory publishers with whom you should be careful.

Whether you should do it is up to you. I'll venture that most people would likely not pay for open access unless they had the funding to do so. If you don't have the money but want to publish open access anyway, you could try asking for a waiver/reduced charges, especially if you are based in a developing country.