You will not lose out on tax efficiency. The wiki does not say to put only bonds in an iRA. Plus you can change your investment in an IRA at just about any time. Typically you are not locked into a specific mutual fund, but can exchange into other funds or CDs or something else when you want.
As for Roth IRA versus traditional IRA, you didn't give enough information for anyone to help you decide. Perhaps it is time to step back and read some books. I will take the liberty and go out on a limb though: You should probably be investing in a employer-sponsored 401(k) or 403(b), too. A suitable investment might be a so-called target-retirement fund for your investments at this time, but it would depend on your goals.
It's all about market timing, uh, I mean rebalancing, uh, I mean opportunistic rebalancing, uh, I mean short-term opportunistic rebalancing due to a short-term change in one's asset allocation.