There is no excuse at all for any collection not to include a fine-condition Willcox and Gibbs. When MS or I are asked which is the most common machine to turn up at antique markets, the answer is W&G every time.
The sheer numbers produced mean that many have survived in first-class order. So, if you are new to collecting and do not yet have an example, don't settle for anything but condition 8 or 9 - one will turn up.
The position of the earlier, glass-tensioner models is very different. Although the later Automatic was introduced in 1875, the company continued to market the glass tensioner at least into the 1880s.
Although not rare by any means, fine examples do seem thin on the ground, and perhaps here it's a case of buy when you can and upgrade later.
The attractive W&G treadle, which was probably imported in limited numbers from the States, can add at least double the value of a machine. Watch for its original bronzed finish.