I'm growing six plants from seed. They are the the red stemmed variety from local seeds. They are doing well and growing tall with trellis support. Here's the real question. Should I pinch out the growing tips to make them bushier?

Just saw it on the net...

There’s no trick to Malabar spinach harvesting. Just snip leaves and tender new stems 6-8 inches long with scissors or a knife. Malabar takes to aggressive pruning and it will not harm the plant in any way. In fact, picking large amounts of Malabar spinach will only signal it to become even bushier. If you don’t want or don’t have the room for a lengthy vine, just harvest aggressively.

 

Read more at Gardening Know How: Picking Malabar Spinach: When And How To Harvest Malabar Spinach Plants https://www.gardeningknowhow.com/edible/vegetables/malabar-spinach/picking-malabar-spinach-plants.htm

The six plants are all growing well but as a single stem which I tie off to the support. I wonder if I should nip the growing tip to make it produce more side shoots.

I have to weed these out as I get so many seedlings growing everywhere. 

Ideally, I cut and eat the top when it has reached a certain height. Side shoots develop quickly and I start taking those or just cutting the stem down about 20 cm. As I mention, they are a bit weedy, so I shouldn't worry too much about it. The Thais certainly don't.

Thanks Cooked that's what I wanted to know. The plants are now over a metre high on a single stem and about two metres is as high as they can go where they are now.