CoStar is best for office and retail, and has minimal useful / detailed info for multi-family and hardly anything substantial on other commercial asset classes (self-storage, land, etc.). It also depends on your type of market. They have pretty good coverage for major primary markets, though tertiary markets coverage is very low. For instance, I own the two most prominent office buildings in a local tertiary market and those properties are not anywhere in the CoStar database, not even showing just minimal info.
I do have a CoStar subscription, though have found that our personal market research for multi-family through online sites (Apartments.com, etc.), Craigslist, and local brokerage listings are much more informative, complete, and can be honed much more specifically to align with any particular property you are looking for. For any asset class, including their bread and butter office and retail, you can generally get as good or better info from your local specialist commercial broker and property manager, plus they will give you nuances beyond just the numbers. CoStar has the advantage of you being able to directly slice and dice the data as you want, though. Also, the bigger brokerage and sometimes property management firms will have a CoStar subscription themselves, and they can run informational reports for you if you have a relationship with them.
If you are looking for lease rates and competing property info for office and some retail, then CoStar can be good for that. If you would also like to know new listings that go on the market, that info quality is very low. They regurgitate what is on LoopNet (which CoStar owns) and sporadically add a random smattering of listings that they may come across. Connecting up with a local broker and also getting on the email lists of the local and national major brokerages, MLS, etc. will give you far more listings, and those are free resources. Similar to the data, the for sale listings are mostly office and retail, with hardly anything useful for multi-family.
Also, be aware that their platform is un-user-friendly. For example (among others), even in this time where 55+% of emails are read on smart phones, CoStar completely prevents users from seeing for sale listings on a smart phone that they email via daily notifications that meet your criteria. They require you to have an app on your phone plus log in to that app AND have the site on your separate computer and be logged into that, AND you have to use your phone to scan a barcode that is displayed separately on your computer screen at the same time to be allowed to see any info. It is the most ridiculous system I have ever seen, and organizations such as banks with far more valuable info do not have these kinds of barriers in place. They claim that they put up all these roadblocks for user account security. The real reason is that all of these extra steps make it almost impossible for you to share your expensive account username and password with someone else, thus protecting their income stream.
Also be aware that they lock you into a one year minimum subscription with no ability to try it for any short period of time on your own. And even if you are dissatisfied with the service, they are adamant on making you pay for the entire year, with no exceptions. Their salesperson can lead you through a real time, personalized, webinar-style demonstration. Be sure to ask for very specific scenarios, locations, and property types that you are interested in since their canned demos only show CoStar in its best light and none of its missing holes. Unless you are using it on a regular basis and are a large scale investor, CoStar would be higher value if they allowed a one month/as needed subscription so that you could jump in when needed and determine if it can provide any value for your scenario for longer term or other times.
So, overall CoStar is an "it depends" resource. It can be helpful, especially for office and some retail. My personal experience is that it costs more than its actual value, and the other sources mentioned above are far better if you have interest in commercial (5+ unit) multi-family and other asset classes that they do not effectively cover.
