TGW's articles on California law tend to follow what I personally consider a fairly airtight interpretation of California law, as written in the penal code. Other folks have other points of view, frequently more conservative but sometimes less so. Significant sources of dissenting opinions are listed here - folks are welcome to read these folks' opinions, read the ones written on TGW, and draw their own conclusions on who they feel more comfortable in following.
California Bushmaster / GB Sales and Evans Gunsmithing / Shooters' World
GB Sales, aka California Bushmaster, has an interesting history. While they're well known in Calguns circles for being against all of the various compliance devices used on off-list lowers, their "get the DOJ to approve everything" approach has inadvertently been a great aid to the off-list movement. Geoff Barrett is their primary salesman, and their primary gunsmith is a man named Evans.
A large section of GB Sales' business is with the law enforcement market. They have an assault weapon permit, with which they import assault weapons for both law enforcement and (post-modification) civilian sales.
Ignatius Chinn, former top firearms expert for the former Firearms Division, wrote a letter approving Evans' modified Bushmaster AR-15 rifles. The nature of the modifications, is that Evans welds a floorplate onto the bottom of the receiver. Functionally, these were the same as Bushmaster's later-introduced Carbon-15 top-loading rifle, and the FAB-10, which featured a similar design. My own opinion on DOJ "approval" is summed up at LegalCaliforniaApprovalInformation.
The first generation of California-legal mag lock devices (the ones which screwed the magazine into place, not allowing removal) were designed to emulate, in a way that required a tool to remove (albeit not a dremel!), the DOJ-approved GB Sales rifles. The existence of the GB Sales rifles made it much more difficult to claim that the off-list lowers were substantially different except for in the reduced permanence of the modifications. Therefore, permanence became the center of the DOJ's assault on off-list lowers during 2005-2006. Because no standard of permanence was codified anywhere in the penal code, this was a far harder fight to win than it would've been had the GB Sales rifles not existed.
GB Sales' California-approved weapons were extremely significant because they used listed receivers. This created an interesting conundrum: technically speaking, GB Sales' rifles were assault weapons due to their make and model, regardless of their configuration. Had they been legally remanufactured by a class-07 FFL, this would have been one thing. But the GB Sales receivers weren't remanufactured, simply modified. Technically speaking, most GB Sales rifles could be interpreted as assault weapons and are in grayer territory than off-list lowers. The end result here is there would be a huge backlash against the Department of Justice if they were to go back on the signed letter sent by Ignatius Chinn, which specifically authorized these technically illegal weapons. This makes it much, much harder to prosecute off-list lowers without having to open the can of worms that the approval letter caused.