What is Panels Simple Cache?

Simple cache is a simple caching module for panels. It provides basic caching through drupal's cache system at different levels of the panels api.

It doesn't really compare to block cache or boost in its job is specific to panels. It caches panes or the entire panel based on you choices in the panels content tab. This could be used on its own or in tandem with Drupals other caches, block caching, boost, or any other cache methods to meet your performance needs.

As far as reliability, its built on top of the drupal cache system so I'd say its as reliable as that... I don't know how you're looking to quantify it.

The simple cache module caches on purely time based criteria; this means that updates to content will not be seen until the next time that it decides it needs to update the cache. It's reliable in the sense that it doesn't need to dirty the cache for anything and cause problems, but it's unreliable in that long cache times can lead to long delays in material. This can really affect how useful it is.

I think the question has been answered.