She has a very weird and complicated set of skill interactions for a role that really just wants good, consistent dakka. Has a funny combo skill with M82 (the bullpup AR, not the RF). In terms of performance she's actually not awful, but she doesn't stand out, and there are enough good ARs to use other than her.

The damage from her skill isn't horrible, but let's be frank, 99% of you won't have reason to use her, and she's more of a meme than a real combatant.

Another one of those funny two-mode dolls. She's actually not an awful damage dealer, but her damage is still less than other dolls that are pure damage dealers. Also, despite having a rifle mode, she can't equip AP rounds so you're stuck with only the AP stats you get from her skill.

She might have use in some formations (mostly shenanigans), but most people probably won't use her.

After literally years, M4 demonstrates WHY SHE IS THE HEROINE and becomes METAL GEAR.

She keeps all her old benefits but has 5 star multipliers and better stats now. This gets even better when Mod3 when she gets a unique that ups her firepower and ALSO gives her armour, so she can kinda tank in a pinch. Her buff tiles are ALSO slightly improved. Her mod 2 skill also tags enemies and enhances the mod skills of other Anti-Rain units.

The big thing however is the desperation mode. At mod2 onward, when 3 or fewer allied dolls are in battle (you can retreat 2 units to force this, or simply deploy her with a partial strength echelon), she pulls out the portable cannon and proceeds to deal hilarious damage that makes grenadiers wet their pants, as huge AoE blasts firing from every dummy. The blasts are kinda 100% accurate (the main hit can never miss, even at night, but the splash damage can. Its weird), and can partly crit (its complicated), and is meant to be a last ditch thing to save a fight under dire circumstances (of course, we instead abuse it). This is however, a doubled edged sword, as her RoF also goes down, so its possible for some enemies to slip by if you havent taken this into account.

Basically, Mod her first. She's pretty much priority #1 for modding.

I struggle to find something nice to say because I legitimately forgot she existed. She has one of those experimental skills that might have some value, but isn't enough of a game-changer to really displace current normal tactics and strategies.

She's not bad. Actually, to be honest, she has better DPS than Lee-Enfield until Lee's special equipment is available, and is pretty reliable. However, she is releasing after other rifles have come out on EN like R93 and M14mod that supplanted her on other servers, so she might not be a priority for you depending on what you have.