Why is there such a big difference in the quotes for Thermo Fisher and NEB restriction endonucleases?

The price gap you're seeing is nearly double, so first confirm whether it's the same specification, same tax, and same packaging. Agent channels, whether cold chain is required, invoice points, and shelf life all affect the price. With 20 restriction digests a month, a single tube can last quite a while. I suggest having both agents quote based on cost per reaction, and clarify the U/µL, number of reactions, and whether buffer is included. NEB-HF and Thermo Fisher's high-fidelity versions do not have completely identical system compatibility when performing double digests in a universal buffer. Before switching, use the same vector to run a double digest comparison and compare ligation efficiency—this is more reliable than simply comparing unit price. If the budget is tight, you can switch only one of the enzymes or buy the smallest package for a trial, but don't stock up in bulk just because the unit price is low.

Whether it is worth switching depends primarily on the cost of your vector construction failures. Twenty reactions per month is not a large volume, and the savings per tube are often less than the labor, reagent, and sequencing costs of a single cloning repeat. I recommend purchasing one smallest package from each brand and performing a head-to-head comparison using the same batch of competent cells and the same vector, focusing on recovery concentration after double digestion, the number of colonies after ligation and transformation, and the accuracy rate of inserted fragments. If you are doing simple plasmids, the difference may be difficult to demonstrate; if you frequently perform multi-fragment or low-efficiency ligation, stability should be weighted more heavily than price. On the supplier dimension, also consider whether technical support can provide batch CoA, return and exchange responsiveness, invoicing, and payment terms. If the budget is tight, you can negotiate a trial price for small packages; do not stock up all at once.

Thermo Fisher enzymes like these have a Fermentas FastDigest background, and batch-to-batch consistency is usually acceptable, but I would not recommend switching everything over just because they are cheaper. For lead times, you need to ask the distributor about real-time inventory. Commonly used EcoRI-HF and BamHI-HF generally have domestic stock, while small-pack sizes may also be out of stock. I suggest first requesting the smallest pack size or a trial sample and running three parallel batches for validation: completeness of digestion on the same substrate, overnight digestion to check for star activity, and colony count and positive rate after ligation and transformation. If the data show no difference from NEB, then consider switching. A usage of 20 times per month is not large, so pay attention to aliquoting and storage to avoid repeated freeze-thaw cycles; batches with short shelf life may lose activity before you finish them.