Disclaimer: I used an AI tool (DeepSeek) to polish grammar and wording only. All opinions, testing, and conclusions in this review are my own.
Recently got the GameSir “Taco” — overseas price is around $35, but I used a coupon in China and paid $15 (retail price $21). I didn’t expect much, but after testing it, here’s an objective review.

What it is
GBA SP size, 62g. Instead of stretching sideways like most phone controllers, it clips your phone vertically. Yes, it blocks part of the screen – a deliberate trade-off for portability and that GB-like feel.
Retro games that fit this format (d-pad only, no analog stick needed):

GBA: Metroid Fusion, Castlevania, Pokemon – set screen to 1:1 or original ratio
DS: DraStic emulator with dual screens stacked – physical buttons plus touchscreen
Arcade vertical shooters (TATE mode): Dodonpachi, Raiden, 1942 – mini TATE setup
GB/GBC: Native ratio, no stretching
NES/SNES/Genesis: Works fine, but black bars on sides

Specs
Bluetooth, 600mAh (claims 30h), wake-up support
D-pad and ABXY rubber membrane, shoulder buttons metal dome
Works as regular Bluetooth gamepad without phone
Comes with protective case, charging cutout
No headphone jack
Downsides

Ergonomics: Modern phones are heavy. Top-heavy, shoulder buttons easy to mis-press. Hand fatigue after an hour.
Software: Their app is clunky. Screen scaling is manual to avoid blocking content.
Charging: Use ≤30W chargers – fast chargers might damage it.
Build quality okay, not premium. 3-month exchange policy (China only? Not sure).


Why vertical? That’s definitely the worst part. Maybe for DS games, I guess. The SP always gave me cramps for its thin design, and I’d hate to hold my phone with both hands.
Back when I was still buying new phones every time my old phone broke (so about 11 years back) I always liked the idea of a slide-out controller instead of keyboard for a touchscreen (just any modern) phone. Sony did the Xperia Play way back when, and if I was looking for a new phone at the time, I’d have gotten it. Nowadays I don’t even think they make the slide out keyboard phones. The next best thing I had was a little phone brace at the top of a bluetooth controller. It games great, but you it isn’t nearly as fast nor as portable. And even then I haven’t used it in a long time.
If I did still use it, I’d probably want one of these, and I think the price seems good. But I would also definitely look for a horizontal product, first.