Both tools solve the same surface-level problem: you want to go live on more than one platform at the same time without running multiple OBS instances or paying for multiple encoders. Restream is the default answer for this — they've been doing cloud-based multistream for nearly a decade and they're the brand most streamers reach for first. VPE is a newer option that solves the same problem with a completely different architecture: it relays your stream locally, on your own PC, instead of pushing through a third-party cloud.
The architectural difference is the entire story. Restream takes your single OBS output, sends it to their cloud, and the cloud re-distributes (or sometimes re-encodes) it to every destination platform. Your PC sends one stream to Restream; Restream's servers send N streams to N platforms. That's convenient — you don't need much upload bandwidth and you don't need to think about anything past 'point OBS at Restream.' But you pay for it in latency added in the cloud hop, in subscription fees that scale per platform, and in the fact that the entire multistream pipeline now depends on a third party staying online.
VPE flips it. Your PC connects directly to each platform's RTMP endpoint and sends N streams out the door simultaneously. There's no cloud middleman. You need more upload bandwidth (the math is below), but the latency added is zero, the recurring fee is zero, and the multistream pipeline survives if any single platform — or Restream itself — has an outage.
Neither approach is universally better. The right answer depends on your upload bandwidth, your latency sensitivity, your platform count, and how much you care about not depending on a SaaS for your distribution.