What do you think of the Singapore savings bonds? Should we purchase it?

It is still a good savings instrument. At least better than fixed deposit rates. If you intend to have a portion of savings or a warchest for investment, the SSB is a good place to park the cash.

If you are using DBS multiplier high interest account, the interest from SSB also counts as a category.

Hi there!
Hmm, perhaps it would be of added-value if you included some context in your question, SSB as opposed to Savings account, then without a doubt, since SSB is risk-free but SSB as opposed to REITs then perhaps not so, given how REITs (for the first half of 2019) actually outperformed the STI index constitutents.
With Fed lowering interest rates, I believe one will see the returns of SSB going lower as well and with the lowering of interest rates, REITs with variable interest would see increase in prices given how more of their income will be allocated as distribution to shareholders :)
To answer your question, I would recommend you to segment / allocate your money into various asset classes so as to diversify your risk and ensure liquidity of your assets at the same time. Hope it helps!