The logic for Logmein is the same.
They contact you (by phone/email/whatever). You supply them a URL with a specific ID. They run the app from the logmein link. They agree to let you take over. You take over. Add to that a chat window also.
When the session closes there is no footprint on the client machine. The client has to run something. Of course you could use windows built in remote assistance ... not something I've ever tried.
Following this link
https://secure.logmein.com/roadmap.asp?decision=0I guessed the following ...
Support Other People's Remote PCs/Servers
I need to connect to the computers over the Internet.
On-demand, incident resolution
They suggest
Instant remote support - no preinstalled software required. We recommend:
LogMeIn Rescue for on-demand remote support and incident resolution. Use a web-browser to gain remote desktop control instantly - from/to anywhere in the world with an Internet connection - without leaving installed software behind. Powerful Admin Center, multiple ways to connect with a remote PC, Mac or smartphone and flexible pricing options meet the needs of virtually every remote support organization.
Available Subscriptions
: Per technician Seat (Annual Agreement) - £58.25 /month
Requires annual payment of £699.00 for 12 months service, recurring until cancelled.*
: Per technician Seat (Monthly Agreement) - £76.00 /month
Requires monthly payment of £76.00 per month service, recurring until cancelled.
I can see that if you've already got a pre-paid, pre-wrapped VNC server, then you won't want to pay for anything again.
You say the picture quality is not great. Maybe you've got your system set to a different resolution and the client has a greater resolution and your system is shrinking to fit, or your system is showing less colours.
I've used Ultra/Real/Tight vnc and never had a image quality issue. I currently handle around 140 pcs on our lan.