It's as safe as the installer makes it. Can it be done poorly? Sure. But it can also be done safely. The normal clutch, brake inputs will cancel the CC.
I have a McCruise in the garage, installed on the wife's BMW. It's a thorough kit, but also uses vacuum & magnetic speed inputs, rather than electronic inputs from the bike's own speed sensor. Personally, I feel it is too expensive for what it is, and I have the Rostra on my S10, though I do need to finish the install.
I know people that have crashed bikes. No CC was involved. That doesn't mean they are unsafe. The bikes or the riders.