It's critical to ensure that employee's monies are correctly allocated to their accounts, especially for participant-directed accounts. All large providers or consulting firms will have computer systems for tracking and administration. Fees are often negotiable. Investments can be pooled or participant-directed. You need to take their overall financial sophistication into account.
Most firms provide a range of mutual funds with different risk profiles and investment objectives.
Showing employees how participation can help them save for retirement will increase participation. Large integrated providers, such as the brokerage firms like Fidelity, Merrill Lynch and Schwab, combine all these capabilities. However, many businesses prefer to use a different organization to plan and administer their plan. There may be limited negotiation in fees since they keep fees down using subsidies from profits they make on investments. You still need a separate investment company, so you lose the benefits of one-stop shopping.