It depends on your business but in my experience, the best was to do a half and half model where some of it was virtual and some of it was onsite. After hours is something that costs effective outsourcing to a virtual company can be effective.
Managed Services have been around an awfully long time...I was bizdev manager for a full service IT firm 10 years ago and the market was mature enough back then.
What's the purpose of your question? Are you looking for market validation? Looking for clients? Pain points? Feel free to edit your question if that's possible, or message me with more detail, and I can give you a more focused answer.
Any smart business owner who can find a reputable and reliable outsourcing service that saves them both time and money would hire such services.
Naturally there has to be caveats to this. Homework needs to be done on the company. Positive relationships need to be built and they have to be able to perfectly understand not just your needs but your company culture and aims.
If you're able to free up time to provide better customer service/find new clients and save money in the process the question would be why wouldn't you do it?
I've worked for a Managed Services Provider in the past and I can say that outsourcing your IT works well for companies with 100 employees or less who are basically centralized in one or two locations. Any larger employee base than that or multiple locations tends to pose logistical problems. MSP's (especially smaller ones) have difficulty servicing remote locations. Most times they are forced to contract out to freelance IT people and you never know who will show up at your doorstep to help "fix" your IT issues.
If it saved you both time and money, then yes.
I'll give you the perspective of running a small services firm not in the technology space: instead of doing IT internally or hiring a couple of people full-time, we found a managed service provider with a good track record and contracted with them.
Most of these providers will have multiple support options available and you can find one that fits your budget and needs easily. Most are also happy to come present to you and you can choose which you like best.
In our case we had:
* Full 24x7 email and messaging access to the provider.
* Monthly visits to our offices to perform on-site checks and maintenance.
* Ability to request larger projects etc at additional cost.
This worked amazingly well and was worth every dollar spent.