>I recently had some work done on my computer and the techs installed a trial version of malwarbytes.
>It's nagging me to buy it.
>Do I need it with Windows 10?

Probably not.

It's a well-regarded security product. It got its start, and is arguably still focused on "grayware", also known as PUPs: Potentially Unwanted Programs. These are apps which purport to, or actually have a useful function but behind the scenes do nefarious things - online shopping "assistants", "coupon finders" etc. Mainstream antivirus often won't identify or remove them because the user may actually want or need the "functionality" but MBAM identifies them and gives the user the chance to remove them.

When first evaluating a new (to them) computer, many support personnel (myself included) use the free version to look for PUPs, report them to the customer if found, and remove if the customer doesn't know they're installed or isn't using them. In most cases diagnostic tools like MBAM will be uninstalled after use (if not already present) but that may not have happened in your case.

MBAM Free does a lot of good so it's completely reasonable that it asks for financial support when the free trial period ends. You can uninstall it from Control Panel...Programs and Features or Settings...Apps if you no longer want it and want the nagging to stop.

As the Wiki article https://en.wikipedia.org/wiki/Malwarebytes_(software) points out, MBAM got its start as an on-demand/batch scanner. If you want to buy it, I recommend against using its real-time scanning option because having multiple active real-time AV scanners is almost always a terrible idea.

As long as a typical business user practices reasonable computer/IT security hygiene, they typically don't need advanced real-time AV scanning. Pretty much any business-grade security product is fine. In some ways vigilance is more important than AV because the latter won't stop zero-days but the former can prevent compromise attempts.