Technology
Rebalancing tools exist because the arithmetic is trivial and the bookkeeping is not. What separates them is what happens to the exceptions.
Rebalancing tools exist because the arithmetic is trivial and the bookkeeping is not. Any advisor can work out what a portfolio should hold. Doing it across several hundred accounts, each with different cost bases, restrictions, cash needs, and tax situations, is a different job.
Matters: how it handles the exceptions. The account with a restricted position, the one that needs cash next month, the one where a trade would realize a gain the client cannot absorb. Every system rebalances a clean account. The difference between them is what happens to the messy ones.
Matters: the audit trail. Why a trade happened, what the portfolio looked like before, who approved it. This is the part you will need on a day nobody is thinking about software.
Demonstrates well: the drift dashboard. Pretty, immediately legible, and the easiest thing in the category to build. It tells you a portfolio is off. It does not tell you whether acting is worth the tax cost.
Whether you should be doing this at all. Rebalancing is real work with real risk and no client has ever chosen a firm because of how its trades are placed. Firms that keep it in-house should be able to say why — and "we have always done it" is not a reason, it is a habit.
The honest test: if the person who currently runs your rebalancing left next month, what would happen? If the answer is uncomfortable, you have a key-person problem wearing a software costume.
Write down the tolerance bands and the rule for when drift triggers action, because an undocumented rule is not a process. Decide who reviews trades before they go, and make it someone other than the person who created them.
The question changes from which software to which firm, and the diligence is different: not features but accountability, records, and what happens when something goes wrong.
Questions this did not answer? Ask them directly — that is what the twenty minutes is for.
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