Same - been using only Step One underwear for about three years now - since soon after they launched actually - before they were ASX-listed. I am overweight, so it prevents chafing between my legs and the bamboo fibre construction makes them stretchable and more comfortable to wear than traditional cotton jocks.
My son also uses them, and he's thin, doesn't have any weight issues, but prefers them for comfort.
That said, I'm not an investor in the company and I tend to usually only buy when they are running a decent promotion with good discounts.
The reason I'm not interested in investing in the company is that I believe that they are way more of a marketing company than many people realise. They spend a LOT on promotion and advertising. I think of them like the Red Bull of underwear. They don't manufacture anything themselves - even their warehouse, distribution and shipping is outsourced I believe. The company is basically an advertising and promotion company who outsource everything other than that to others.
That's not a terrible business model - it works for Red Bull and a number of other brands and it means you can run the business from anywhere in the world because you aren't making or distributing your own products - you are paying other companies to do all that for you, and you're just handling the promotion side of things and creating brand name recognition and hopefully repeat sales, and it can be very successful if you get it right and people love your product and keep buying your product.
That said, it's early days for Step One, and I've seen similar situations where relatively young companies float to (a) get expansion capital, but (b) mostly so the founders can get an early pay-back on the time and money they have put into building the brand. And so it's not always a BETTER company after it becomes a public company because a lot of that extra capital just ends up in the founders' and original pre-IPO-backers' pockets (/bank accounts) rather than all providing expansion capital.
So I tend to give them a few years as a public company before I invest in them.
Bottom line for me is while they make excellent products, they are NOT cheap, so you're paying for that quality and also for the brand I think, even though it's a relatively young brand it's also reasonably well known already. And I think the barriers to entry are very low in this space. Probably the main competitive advantage is their effective marketing and the brand name and brand recognition they have managed to build to date, but if someone else was to provide a similar product with similar quality and their gear was just as comfortable and long-lasting as Step One's stuff is, but at a significantly lower cost, which wouldn't be too hard - because Step Ones are SO expensive - then I'd certainly try the competiitors product and would switch for future purchases just to save money.
I don't think there is ever going to be a huge amount of brand loyalty with underwear unless it's like, Calvin Klein underwear and you're a spoiled rich kid. Underwear is chosen on (a) comfort and fit, and (b) price. Step One have the advantage in my opinion for comfort and fit (including that the jocks stretch to fit and move with you), but they do NOT have any price advantage, so are ripe for disruption in my view.
So happy to wear them, but not going to invest in the company at this point (or probably ever to be honest) - they don't have the attributes I'm looking for to be one of my top investing ideas. The main one being a moat that makes it hard for other companies to eat into their market share.
I could be wrong, and they may do very well (like Guzman y Gomez might, and I'm not going to invest in them either for a lot of the same reasons even though we buy GyG burritos every week), but you can't pat all the fluffy dogs, and I only have so much capital to invest, so I have to stick to my best ideas.
Additional: The main difference between Red Bull and Step One of course is how often people might buy an "energy drink" compared to how often they need to buy underwear. Step One is not an FMCG company - it's definitely more occasional discretionary spend.
