The SB6121 is a DOCSIS 3.0 4x4 modem rated for 174mbps, SB6141 is a 8x4 rated for 343mbps, and SB6181 is a 16x4 rated for 686mbps. Outside of their capabilities, the hardware on them are nearly identical. There is nothing "EOL" about the SB6121 except for the idea that it's unable to support 200mbps. It's a perfectly good entry-level modem capable of offering speeds that are over 7 times the minimum definition of "high speed internet".