About try.desync.com

try.desync.com gives you a web-based shell on a dynamically-allocated instance.

There are some differences from a normal instance, though. Specifically:

The host is a VM.
The host usually runs a development snapshot that may be unstable. You "get" to help us test, Aperture Science style.
The host kernel has various debugging facilities enabled, which hurts performance.
Network connections are limited in terms of concurrency.
Network traffic is limited in aggregate throughput.
Only outbound connections are allowed (except TCP port 25, which is never allowed).
The Basis image is a customized FreeBSD that includes some tools like curl and mtr.
SSH host keys are pre-generated (and thus, shared) to reduce startup time.
The broker's SSH keys are preloaded, rather than having to wait for desync-provision to run.

The session broker (Zuul) places some limits on number of concurrent sessions beyond the normal placement limits imposed by the API, mostly by client ASN and/or subnet. The idea is to prevent one person from hogging all the sessions, which might also indicate that some mischief is afoot.