We have been using Zoho Assist for awhile and like it. We use both the 'unattended access' on select machines as well as the 'on demand remote support'. Both work well and are included. You can even reverse the screen to show the customer something or have a mini webinar. One feature that I have not tried, was the the mobile app.
We have a university that we do a lot of work with. They have Cisco VPN deployed. Which we use daily and it works great. However as of late I have found that when you have more then two virtual adapters (doesn't have to be a VPN. It should be another software) installed they can fight with each other. So that is a potential concern.
Ultimately I prefer the 'service provider' route versus VPN. For the following reasons.
1. I can use with any customer. You might get a corporate customer that doesn't want additional equipment on the network.
2. Adds no additional per job cost. There is a monthly flat rate, of course, but no equipment cost to think about or install.
3. You can see the screen. So if customers have a problem you can both see it. Additionally we use this for training's all the time.
Either way being able to remotely administer systems remotely is a lifesaver for everyone.