Hi - I think the original Call Guardian 301 was released circa 2015 and it had a different form factor for the answering machine base station, it was on the right hand side of the base station vs answering machine function at front of unit on the MKII version. The MKII introduced a Call BLOCK button in between the left and right menu selection keys and a raised OK button. Maybe an upgrade to internal printed circuit board - unaware.
Apart from the physical differences, in the past, forum posts have indicated the following annoyances with both Call Guardian models which may not impact everyone.
1. No ECO or ECO + Mode
2. Volume button from 2 to 5 setting doesn't increase volume significantly
3. Test Messaging no longer supported on PSTN - unsure if that should say full stop before PSTN.
Both units were sold by British Telecom as well, the BT8500 and BT8600 equivalent versions are no longer available for sale in the UK possibly indicating a trend that Telstra may follow one day. If Call BLOCK on handset is important to you, the Telstra TEC-C and optional additional cordless phone, the TEC-A feature a dedicated Call BOCK button but have a different key layout to the MKII; they are made by the same manufacturer, but Telstra has not included an Answering Machine with the Base Station - perhaps a future offering.
It may pay you to do some research on other options in the market or ask Telstra if the TEC-C will have a MKII version with Answering Machine available soon. Call blocking is also possible to achieve in the My Telstra App, 24x7 Online Account and in the Arcadyan LH:1000 Smart Modem if you don't require an answering machine. In that scenario you would pair a DECT CATiq 2.0 phone like the Telstra Smart Handset-Cordless (TSH-C) directly to the modem's internal base station.
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