Good, if deployed properly.
My employer deployed Wyse terminals to our communal staff areas to replace standard Dell desktops which were due for end-of-life replacement.
The only problem is that while we can carry out simple tasks such as checking fault logs and reading emails, it is useless for certain very important tasks required in my field.
Much of our field equipment (deployed during the early-mid 1990's) can only be interrogated via a dial-up telnet connection. The Wyse terminals are incapable of this. Also, rather stupidly, they send us our monthly video briefing by DVD, the Wyse terminals don't have an optical drive. There are many other safety critical tasks which the terminal cannot perform.
Also, due to the very remote location of our base, our corporate network access is very slow (<1Mb/s), which results is app access being ridiculously long. It takes 2 minutes to open MS Word alone!
Our manager tried to have the terminal replaced with a desktop, but IT refused on grounds of policy. Eventually he got round it by requesting a personal issue laptop for himself and then donating it to our cause.
It would seem that some IT managers have blind ambition to save power and cost with these terminals, but if in turn that means I cannot get the equipment up and running as I don't have the means to remotely interrogate the it, then any IT savings will be swiftly lost in compensation payments to the customer.