Bondtech Prusa I3 MK3S+/MK3S / MK2.5S Extruder: Review, Pros & Cons

Summary

A 3:1 geared BMG extruder upgrade for Prusa i3 MK2.5S/MK3S/MK3S+ that reuses the stock All Metal V6 hotend and needs Bondtech firmware plus a new X-carriage. Check hotend compatibility before buying: it fits only the original V6, not the Mosquito variant.

Strengths

3:1 BMG drive train with a lighter 291.5 g moving assembly (51 g / 15% less than stock).
Owners report easier jam clearing and better flexible-filament handling than stock.
SLS Polyamide 12 housing; reuses stock Prusa gears, magnets and hotend.
Bondtech supplies adapted firmware with E-steps and Z_MAX changes.
Works with MMU2s/MMU3 when the extra add-on is used.

Weaknesses

Fits only the original All Metal V6 hotend; it is not a hotend upgrade.
Requires a replacement X-carriage (printed or purchased) and Bondtech firmware.
Firmware updates lag Prusa releases by days to weeks.
Several owners report no visible print-quality difference versus stock.
At least one owner reports jam-prone behavior (possibly assembly error).
Warranty term and individual replacement parts were not verified.

Verified specifications

Product	Bondtech Prusa i3 MK2.5S/MK3S/MK3S+ Extruder upgrade IDGA, article EXT-KIT-68, EAN 7350011410651.
Compatibility	Prusa i3 MK2.5S, MK3S, MK3S+ with the original All Metal V6 hotend only.
Gearing ratio	3:1.
Extruder	Bondtech BMG (Mini Geared) drive train.
Stepper	25 mm pancake, 18 N/m torque.
Max input current	0.8 A.
E-steps	415 at 16-bit microstepping; 830 at 32-bit microstepping.
Weight	291.5 g net (incoming parts), 380.2 g gross, 343.2 g stock parts removed, a 51 g (15%) saving.
Max chamber working temperature	80°C (stepper limit); HT PLA sensor parts 60°C (90-100°C if annealed).
Housing	SLS printed parts in Polyamide 12.
Firmware	Bondtech adapted version required (E-steps and Z_MAX 205 mm changes).
Licensing	GPL v3.0; STEP files available.
MMU2s/MMU3	extra add-on required.

Full research notes and sources

What it changes

The kit swaps the stock Prusa extruder for a geared 3:1 BMG drive train on the same V6 hotend. The moving mass drops 51 g (15%), from 343.2 g to 291.5 g, and the 25 mm pancake stepper is rated at 18 N/m with a 0.8 A max input. Because Prusa’s stock extruder already uses Bondtech drive gears, the gains here are the geared reduction, lower mass and easier disassembly rather than gear material. The kit does not include a hotend, and it reuses stock Prusa primary and secondary drive gears, magnets, hotend assembly and PTFE (cut to 6.30 mm from the hotend metal face per the install guide).

Owner experience

Owners in the Prusa3D forums and r/prusa3d report better handling of flexible filaments and fewer jams, easier disassembly for jam clearing, and in one case zero jams over a year. A few owners report slightly better surface homogeneity from the lighter moving mass. On the other side, several owners report no visible print-quality difference versus the stock extruder, and at least one reports jam-prone behavior that may be an assembly error. Flexible-filament issues persist in some setups, and MMU2 setups can need IR sensor tuning. No instrumented independent test of this exact kit was found; the available evidence is owner forum posts plus one affiliate-style upgrade roundup.

Firmware and upkeep

The kit needs Bondtech’s adapted firmware: E-steps change to 415 (830 at 32-bit microstepping) and Z_MAX changes to 205 mm, with a slight drop in Z height. Bondtech forks Prusa firmware, so each Prusa release arrives days to weeks later, and not every change is E-steps-only (Z_MAX and mmu.cpp adjustments are involved). Upkeep follows the install guide: correct PTFE path at 6.30 mm, adjusted tension lever, correctly oriented magnets. The kit reuses stock Prusa gears, magnets and hotend, so many spares are standard Prusa parts, though Bondtech does not publish a full parts list for this kit on the captured page. Warranty terms were not stated on the captured manufacturer page.

Is it worth it?

At the observed Bondtech direct price of $110.00 (on backorder at capture), the kit is a reasonable targeted upgrade for owners who print flexible or abrasive filaments or want easier jam serviceability. Above about $130 from third-party sellers, weigh it against the stock extruder, which already uses Bondtech gears, plus the cost of printed or purchased X-carriage parts. The kit is not a hotend upgrade; users wanting hotend changes should look at the Mosquito variant (EXT-KIT-69) or separate hotend kits. Price observations: Bondtech direct $110.00 (on backorder at capture), 3DPrima €137.90 (in stock), TAW Global $129.99, and Ultimate 3D Printing Store lists it (price not captured). Recurring costs are filament, nozzles and PTFE tube (a spare is included); firmware updates are free and there is no subscription lock-in.

Which model this is

This page covers EXT-KIT-68, the Bondtech Prusa i3 MK2.5S/MK3S/MK3S+ Extruder upgrade IDGA, EAN 7350011410651, compatible only with the original All Metal V6 hotend. A Mosquito-hotend variant (EXT-KIT-69, EAN 7350011410675, 378 g net) shares the same 3:1 BMG drive train, 25 mm pancake stepper, 415 E-steps, 0.8 A max input and 80°C max chamber temperature but differs in weight and hotend compatibility. The Amazon listing B099NWFBFR is reported as the Mosquito variant (EXT-KIT-69); whether it is actually EXT-KIT-68 or EXT-KIT-69 was not confirmed. ASIN B099NWFBFR.