AIUI power tapping on the SX3 uses a jog button on the end of the downfeed handles.
You can't always assume the OEM from appearance, for example apparently identical mini-lathes can be built by either SEIG or Real Bull and apparently are based on the same original Russian design.
I know Arc & Axminster sell SEIG products, but some of those other suppliers do too, but I can't speak for those mills. NOt sure if Chester don't stock one of the second type as well.
Finally don't assume two that look the same are the same, check specs and not all differences are visible or on the spec sheet (e.g. they may have different electrics or use different ways to spec motor power, for example).
Specs won't tell you much about spares stock or customer support either. Best to make a shortlist then speak to the companies who sell machines that appear to meet your needs.
Neil