These two events happened in relatively quick succession. I started getting questions about positioning because at first glance, it looks like they might be contradictory. In fact, they solve two, very different customer challenges.
Twinstrata is all about leveraging the cloud for storage, and keeping your compute local.
ExpressRoute is all about leveraging the cloud for compute, while keeping control of your storage.
So, if your customer is looking at cloud to provide fourth (or fifth) storage tier, Twinstrata fits the bill.
If your customer is looking at cloud to augment (or replace) their compute, but don't want to (or can't) leverage cloud for their storage, then ExpressRoute is part of the answer (at least for Azure). I believe this has a wider variety of use cases, as there are more numerous obstacles to cloud storage than there are to cloud compute. These range from data availability SLAs, data governance issues, regulatory pressure and so forth.
We should also remember that there are uses for low-latency, high bandwidth links into public cloud provider data centers. And it's worth noting that Amazon and VCHS have similar offerings - both uninspiringly named "Direct Connect". I guess Microsoft had a little extra left in the tank to name their offering.