Being one of the lucky few to get my Steam Frame a few weeks ago, I have been using it quite a bit since then. I have been buying some third-party accessories to mitigate some of its weaknesses.
First the obvious one: it is surprisingly light and small, but overall not comfortable enough due to my glasses. To solve that I went ahead and bought prescription lenses from VR Optician (119€ including fast shipping and additional prescription fee).
Then I figured I had better protect it against sunlight because I do not have one of those fancy head mounts nor do I want to pack it in its box between each use. Thus I got an AMVR lens cover that fits quite well (13€).
And finally the battery life situation is... Well it's bad. I got decent VR legs and can play for hours, but the battery only lasts at most 1h30 when running PCVR at 120Hz. So I got myself a UGREEN Nexode 145W 25000mAh Power Bank (56€), 2 short angled USB-C cables (24€), round magnetic USB-C adapters (16€) and a small fanny pack (10€).
I will also say there has been some trial and error regarding the magnetic adapter. The idea is to protect the headset port in case the cable snags on anything. I wanted to plug it directly in the headset port, but it tends to disconnect when I turn my head. The tradeoff I landed on is : one very short cable plugged in, magnetically coupled with a longer one that goes to the battery. The 240W-rated USB-C cables are also overkill but hey, not that much of a price difference (they are quite thick though and contributed some in my disconnect issue).
So there you have it, 238€ on top of the initial Steam Frame + ergonomic accessories kit purchase (which is a must-have if you ask me), not counting said trial and error.
Update: there are strong arguments in comments against using magnetic adapters. I'll be ditching that and keeping the 2 cables approach so that there is a straight connection (hopefully weaker than the angled plugs) that can unplug more easily than the battery or headset side if the cable snags on something.
I had heard from reviews that the top strap was basically not needed. Then I tried it for myself. What it does is alleviate the pressure on your cheekbones as the headset no longer sags and allows you to loosen the horizontal strap a little, also lessening the overall pressure on your face.
It is not needed in the sense that the headset is wearable and has that "ski mask" look without it. I for one will never be taking it off.
I haven't noticed any pressure there, but of course everyone's bone structure is different, which is part of what makes VR headsets so hard to make!
I did read some info online in the months before receiving mine and many people suggested moving the rear further up on the head, which might alleviate that pressure.