There's no reason they should lose flexibility in terms of hours. That's just made up stuff that Uber puts out to try to make their argument.

If you drive more than 30 hours per week or 120 per month for one company and meet the 5 criteria, you should get benefits and be taxed as an employee for that period from that company, unless you are already receiving benefits from another company.

There is no reason to prevent them from logging in and out when they want.