Ideally ELNs should be implemented as part of a well thought out data management strategy for a research group or lab.  Considerations for choosing the best ELN for your needs are listed below.  

• Cost - ELNs range from free and open source to commercial implementations that can be charged on a per month per user basis.  Most paid versions charge academic users ~$10-20 per user per month.
• Functionality - not surprisingly, free options provide fewer functions and may restrict the number of users.  More expensive commercial platforms will generally provide a higher degree of customization and more security features.  Other considerations include version control, whether pages can be locked and electronically signed and what kind of data storage is needed to meet government or funder requirements. 
• Access and collaboration vs security - most ELN platforms are cloud-based, providing researchers flexibility and mobility for entering data outside of the lab.  Collaboration and sharing of data can be done with pdf's or reports created from within the ELN or as a feature of the ELN.   A hierarchy of roles such as contributor, reviewer, editor determine who can see and approve project records.  After the work has been reviewed, the record is locked to prevent unauthorized changes.  

Some types of research may dictate that an ELN have specific features.

• The Health Insurance Portability and Accountability Act (HIPAA) governs medical information.  Human subject research may require data security measures that are HIPAA compliant.
• Similar data privacy measures may be necessary to meet the requirements of The Family Educational Rights and Privacy Act (FERPA) that governs educational information
• Some other features that might be necessary include the ability to meet audit, reporting and electronic signature guidelines.  See Part 11 of the US Food and Drug Administration guidance document as an example (previously  21 CFR Part 11; Electronic Records; Electronic Signatures, Electronic Copies of Electronic Records).

The use of ELNs to support invention disclosures has not been extensively tested  in the courts.  Though the US moved to a "first inventor to file" system rather than the first to invent, lab records are still important legal documents to support patent claims.  At Oklahoma State University, an inventor is anyone who contributes to the idea or conception of the invention.  This may be documented with the lab notebook.  More information about the OSU disclosure process is available from the Technology Development Center and the OSU IP Policy.

Tremouilhac, Pierre et al. “Chemotion ELN: An Open Source Electronic Lab Notebook for Chemists in Academia.” Journal of cheminformatics 9.1 (2017): 1–13. Web.