<Anecdotally> I've formed three series LLCs (one in IL and two in DE.) The first two times, they were basically used to register investment fund families so that each individual fund didn't have to be registered. We saved a significant amount of time and money in the long run, but we used legal and tax professionals that have expertise in using series LLCs for EXACTLY that purpose. The team had securities attorneys and compliance officers triple-checking our work and we were using it for much more than just saving on basic filing fees, etc. I would estimate we saved in the hundreds of thousands of dollars. But it was a very specific use case, and there have been many mutual fund/investment companies that have went before us and tested the boundaries.
The last time I formed a series LLC it was for almost exactly what you are proposing - a consulting firm/startup incubation company. I just went with my gut feeling based on what I had read on the internet and my prior experience with the fund companies. I had the series LLC formed by an attorney with series LLC experience in DE. I think I paid under $700 for the formation. Overall, it has been a HUGE mistake. The costs and hassles of keeping up the separation of the series (separate bank accounts, separate accounting systems, etc.) has been a pain and has far outweighed any of the benefits gained. In fact, it has been a pain just trying to do simple things like open a bank account for series companies here in IL. Bank officers are not familiar with series LLCs and their systems aren't set up for that, so I was issued company credit cards that have the wrong name on them, checks with the wrong name on them, etc. Branding is a nightmare if you comply with the letter of the law in some states. I just really didn't know what I was getting myself into for this usage scenario. I will most likely have to restructure the companies in the near future for various reasons...probably at significant expense.
As others have said, the series LLC form is not as well-known by the public or as legally tested as other entities. You really should have a great reason for choosing a series structure before you do so, and you should definitely speak with a tax attorney or accountant that has experience in this area. Some of the pros and cons are very easy to misunderstand. If I were doing it again, I would personally NOT use a series LLC for an incubator/consulting arrangement.
The last time I formed a series LLC it was for almost exactly what you are proposing - a consulting firm/startup incubation company. I just went with my gut feeling based on what I had read on the internet and my prior experience with the fund companies. I had the series LLC formed by an attorney with series LLC experience in DE. I think I paid under $700 for the formation. Overall, it has been a HUGE mistake. The costs and hassles of keeping up the separation of the series (separate bank accounts, separate accounting systems, etc.) has been a pain and has far outweighed any of the benefits gained. In fact, it has been a pain just trying to do simple things like open a bank account for series companies here in IL. Bank officers are not familiar with series LLCs and their systems aren't set up for that, so I was issued company credit cards that have the wrong name on them, checks with the wrong name on them, etc. Branding is a nightmare if you comply with the letter of the law in some states. I just really didn't know what I was getting myself into for this usage scenario. I will most likely have to restructure the companies in the near future for various reasons...probably at significant expense.
As others have said, the series LLC form is not as well-known by the public or as legally tested as other entities. You really should have a great reason for choosing a series structure before you do so, and you should definitely speak with a tax attorney or accountant that has experience in this area. Some of the pros and cons are very easy to misunderstand. If I were doing it again, I would personally NOT use a series LLC for an incubator/consulting arrangement.