We're looking at roughly 20 days or so for the HL007 pen, which fits your 3ml retatrutide runs nicely — the dose range goes from 0.01ml up to 0.6ml, adjustable, and it's mechanical, so no batteries to worry about.
It takes 31G or 32G needles, and the injection time is under 6 seconds, which basically means you're not standing around waiting for it to finish. One thing we've noticed is the cartridge inner diameter is φ9.7mm, so you'll want to confirm your vials match that before ordering.

The feedback system is both visual and auditory — you hear a click and see the plunger stop, so there's no guesswork about whether dose went in. Medical-grade plastic throughout, 17cm long, and it's not great for viscous formulations because the narrow needle gauge can clog.

Most buyers go with the standard white labeling, but customiaztion is availble for color and labeling if you need it. We usually have stock, but confirm lead time if you're ordering over 50 units or so — the MOQ is 100 pieces for custom runs.

Actually, one detail that caught me off guard: the device length is 17cm, which is longer than some comparable pens, so make sure your handling protocols account for that. It's better than reagent-grade syringes for this application because teh dosing is tighter tolerance.
Anyway, we're quoting $12.50 per unit for 500 pieces, with COA and TDS included, and our company can ship within 10 working days after PO confirmation.