Here is SJ's response to mulching. I found this on Home Depot's question and answering section. I also emailed SJ and they basically said the same.
Even though we do not claim it to be a convertible mower/mulcher as is, it technically is one, due to the fact that removing the rear bag cause the rear hatch to fully enclose the deck, causing grass clippings to remain in contact with the blade until light and small enough to drop behind the cutting path in the form of mulch. In this way, no mulch plug is needed, yet it converts between a mower with bag and a mulcher.
In the near future, we are releasing a mulch blade kit (model# ION16LM-MB) to further utilize this capability, so keep an eye out for that!
All the best,
Snow Joe + Sun Joe
This was posted 2 years ago and I still see no mulching blade on their site. So not sure what's up with that. I actually bought the mower the other day during HD's sale and mowed my yard yesterday. Utilizing bagger only. It did a fine job and I only used about 1/2 a charge. Seems to be well built and it's easy to use. I plan to mow w/o bagger next time to see if there truly is a mulching like cut. Even if that does not work out well, not a big concern to me as I never have mulched much. Biggest question is how well battery holds up over the long haul. Of course that's the question with any of these.