The 4Nine isn't considered a "beginner" because of the design required to make it short... that being the drop-in, shoulder retained button, the thin magnetic interface and the hybrid pinless style 510 ring.
On clones, the magnets tend to be weak and fail frequently... particularly if resistances used are low, there is poor conductivity (from button to tube - due to sloppy machining tolerances), and the magnets get hot.
A genuine 4Nine.
Zillions of 4Nine counterfeits, at a dozen price points, have been sold... probably because of the clean style, small size and magnetic button. What percentage of that zillion have issues is unknown. Even the authentics have had issues... but Tarsius stands behind those, for the most part.
Ultra short
mods, with few exceptions,
can be problematic... if not made with close and well considered tolerances. The "Red Rod", although not as common as the 4Nine, because to my knowledge it's not been cloned yet, may be one of the more reliable short
mods... and perhaps the "Fortune" as well, although I've not received my Fortune yet and can't say for sure.