I've looked at four of the five collected delves (excepting the 'Pale Reaver'). All include a small map (either by Dyson Logos or Matt Jackson) with a maximum of ten rooms or encounter areas, perfect for a single session. The delves each have one or more suggested setups to help bring the characters into the scene. The small adventures are all very serviceable and creative, with some elements of mystery and exploration.
As an added bonus for later plotting, or dovetailing the delves into a larger game world, each of the delves has a few end-notes with either suggestions or questions to the DM for future thought or adventure threads.
The delves are set up for D&D 5e (and have call-outs or page references to the associated DM's guide and Players' Handbook). However, the setups are generic enough for any OSR, and monsters and spells can be easily converted. Because of the small encounter areas, the amount of translation will take only limited effort.
What the delves each do well, is the third page. Wait - the label on the box said two pages! What is this sorcery? The third page (or Appendix) is a quick and dirty how-to-use guide. The delves are written with level flexibility in mind. Therefore - monsters, traps, challenges, and treasures are written in very generic terms (i.e. 'undead', 'sword') Being 5e - challenges are written with 'DC' terminology in mind, but this is also easily translatable for relative levels.
Additionally, the appendix lays out some guidelines for scaling the adventures to party level and size. This flexibility is a welcome addition and guidance to any small pre-written adventure - especially when a pick-up game or side quest is needed, Yes, there is a small amount of preparation, but with the framework, and a reasonably experienced game master could scale on the fly or with only a small amount of prep time (e.g. the 'spider' in Room 3 can quickly become a 1/2 HP large spider or 4HD Giant Fire Hell-Spider).
So take a look at them, save them in your just-in-case folder, and have fun!