Steering tube extender

[KDean]

Are these safe ? Or getting a new fork that hasn't been cut down better ,it's for a nomad MK2.

[PH]

Yes, if fitted correctly there's no safety issue with them. Two types, internal and external, I'd rather use an internal which is held in place with a wedge, but that's mainly for aesthetics.  The external type clamps the same way as a stem, so is as secure, it's just looks ugly IMO 
How much higher do you need it?  There's some pretty steep stems available, if possible I'd prefer one of these, less joints is always better.
You might also look into having a frame builder extend it, it's a simple job with an internal sleeve.  I had this done, though it was some years ago and I can't remember the cost, I do remember it was less than I was expecting and that was by a well renowned frame builder.

EDIT - I have an Airnimal Joey folding bike, it effectively has a 250mm external steeer extension held in place with a QR fitting, the strength comes from the 60mm overlap.

[mickeg]

If they were not safe, major corporations would not sell them due to the potential liability.

A friend of mine added one to his bike.  Before he added one, I loaned him an adjustable stem so that he could try different reach and height with the adjustable.  I suggested that with the adjustable he could figure out what kind of angle he might want on a stem but he bought a new extender instead of a stem.

Four years ago I bought a new road bike.  It only had 25mm of spacers between the headset and stem, steerer tube was cut for that length.  To get my geometry to match my other bikes, I needed a 25 degree stem, it took some trigonometry to figure that out.  But, I could not find one with that angle and ended up buying a 35 degree stem, I think the one I got is 90mm. 

I also put a 35mm stem on my Nomad several years ago, I cut that steerer shorter to make packing it in my S&S case easier.

First photo is four years old immediately after I changed the stem.  I have 15mm of spacers above the stem, 10mm below.

Second photo is last year after I added the accessory T bar for a handlebar bag.  The T bar consumes all 25mm of space that the spacers previously used.

I mention this much detail because if a 35 degree stem would get you the height that you desire, I would go that way before getting an extender.  I think it looks much better.

You mention it is for a Nomad, thus I assume that the steerer tube is not carbon, I think that an extender on a carbon tube is a no-no.

[JohnR]

I've used Ergotec products for this purpose without problem but not with a heavily loaded touring bike. I think I have a couple in my box of stems if you want me to look.

How much rise are you wanting? You can get stems for angles up to 45 degrees https://www.sjscycles.co.uk/stems/110-humpert-high-charisma-1-18-inch-stem-plus45-deg-318mm-clamp-black/ , https://www.ebay.co.uk/itm/165555271824 .
The safety rating of 5 means "This product is rated to Humpert’s safety level of 5. This means it is suitable for use on road bikes and mountain bikes that have a combined rider and luggage weight of below 100kg as well as hybrid/trekking electric bikes (restricted to 25km/h) that have a combined rider and luggage weight of below 140kg." However, I'm sure that, as there tends to be with German brands, a big factor of safety and it's difficult to envisage a failure mechanism.

One of these stems, if the right size, avoids the separate set of joints and extra weight associated with a steerer extender plus a normal stem. The challenge is figuring out if one of these single part products will put the handlebars where you want them. If you get one, give it some good testing not too far from home.