There is nothing wrong with free unless there is a hidden cost involved. Small business plans that don’t require filing a Form 5500 is great until you realize the cost in saving for retirement plans.
SEPs are a nice plan, but there is no opportunity for salary deferrals and you have to give the same percentage contribution to all your employees. A Simple IRA is nice too, but the deferral limit is a lot less than a 401(k) plan and again, contributions must be pro-rata, which means no greater percentage of contributions to you as owners. A solo 401(k) plan is nice too, but it’s obsolete the moment you hire an employee.
Whatever your situation is as a plan sponsor, you do yourself a disservice by not looking at all the different options of retirement plans out there and seeing what fits you.